I took this from one of my posts on the RPG.DnD.Dark-Sun board that WotC runs, then cleaned it up a bit to fit in with some discussions Samloyal and I had. While I'm anxious to see the official 3e psionics system, I will say that what I have seen up to this point does not impress me. I agree (though somewhat less violently) with Samloyal on this. New comments and insertions are in [brackets]

Truthfully, I'm not overly fond of either [psionic] system. The new system, IMO, robs psionics of much of its flexibility, while the old system completely favored those with high stats, and didn't give nearly enough PSPs. I've long felt that psionics should be much more flexible than magic, but less powerful... thus, while a Wizard or Sorcerer can blow an army off the field, a psionicist can do three or four different things, expending only as much energy as he likes on each effect.

Personally, if I do say so myself, I prefer the system I devised. I'll quickly put it out into 3e stats, since that's what we're arguing about, leading off with the class, Psionicist. [Note that this is an alteration on the SAGA spell-casting mechanic, updated to 3e stats].

A psionicist is a master of his own mental abilities. Through long years of study, a psionicist has learned to harness the power of his own mind to create many effects, from the clouding of minds to the calling of lightning. Each of these effects varies from psionicist to psionicist, so those facing a psionicist can never be quite sure as to what to expect.

Adventures: A psionicist can adventure for many reasons, but most often it is to test and explore their own abilities. While some are content with the life of self-contemplation, many find that they are driven to test their abilities in the world at large. With an evil psionicist, this can lead to great trouble for a world that is usually unprepared for the fruits of an evil imagination; with a good psionicist, those helped often have little idea how a lone psionicist could do so much.

Characteristics: In many ways, a psionicist can be seen as the opposite side of a monk. Whereas monks use their mastery of their physical bodies and wills to achieve great feats, a psionicist achieves her feats through mastery of her mind and will. Their abilities with their body are generally less-well developed, but psionics can increase those abilities beyond their usual level, allowing psionicists a measure of physical ability, as well.

Alignment: While most psionicists are somewhat independent, the strict dedication that their skills require precludes them from having a chaotic alignment. (Addendum for Dark Sun: Due to the high psionic potential of the natives of Athas, and a culture that, in general, supports the study of the Way, psionicists from Athas may be chaotic in alignment.)

Religion: Very few psionicists are actually religious. Given their abilities, many feel that they have transcended the mortal and are "above" such things. Those that are religious often see their abilities as gifts from the Gods, or some innate kinship with the Gods themselves. They therefore tend to follow either creator-gods, such as Moradin, Corellon Larethian, Yondalla, Garl Glittergold, Gruumsh, or gods who favor knowledge, such as Boccob or Vecna. (Addendum for Dark Sun: Like most Athasians, psionicists are rarely very religious. Those that are tend to follow an element that they have gained control of through their mastery of the Way, or be linked to the Spirit of the Land as druids.)

Background: Psionicists have highly varied backgrounds, but most discover their innate potential at a young age, somewhat like a sorcerer. While some few develop their abilities on their own, most often they will either find a mentor in the Way to teach them more, or go on to another profession with their innate abilities being used to supplement those they learn in that craft (be it smithing or wizardry).
Psionicists rarely congregate in groups larger than a master with one to three apprentices. They gain little from the association save the benefit of a fresh viewpoint on the use of their powers, and are often very self-contained, making companionship of others, in their mind, unnecessary.

Races: Psionicists are most common amongst humans, as they tend to be those most likely to have the ambition and drive to learn psionics, and a culture that encourages such experimentation. While elven, dwarven, gnomish, halfling, and orcish culture have no native traditions relating to psionics, a psionicist will occasionally arise out of those races as well. Amongst the evil humanoids, perhaps the best-known psionicists are the illithid, squid-headed man-beasts who use psionics as elves use magic and dwarves use steel. (Addendum for Dark Sun: We all know the above doesn't apply to Athas; everyone and his chihuahua has psionics, and most use them to their full advantage.)

Other Classes: Psionicists, with their lawful tendencies, can work very well in groups. However, their tendency is to be very self-contained and to try to do everything themselves, often leading to a degree of competition with any member of the party whose abilities the psionicist feels he can emulate. They often get along quite well with Monks, as both have somewhat similar interests, but that camaraderie tends to turn into a friendly rivalry, rather than simple joy for their companionship.

Abilities: The mentally-based abilities of a psionicist means that they find Charisma, Wisdom, and Intelligence especially helpful. The Difficulty Class to resist a psionic effect is equal to its Effect Level + Appropriate Stat Bonus + Area of Control bonus (all of which is described later). Like wizards and sorcerers, a high dexterity and constitution can be useful; however, some psionicists can get around the need for such things by increasing their abilities psionically.

Alignment: Any non-chaotic (or any, in Dark Sun).

Hit Die: d4

Class Skills (with the key ability noted in parenthesis): Animal Empathy (Cha, exclusive skill), Concentration (Con), Intuit Direction (Wis), Knowledge: psionics (Int), Scry (Int, exclusive skill), Sense Motive (Wis) and Psicraft (Int; like Spellcraft, but arranged around psionics). Note that psionicists' highly developed extrasensory abilities allow them access to certain skills that would otherwise be exclusive.
In addition to those above, each and every psionic effect is considered a class skill (usable untrained) for psionicists; a psionicist may devote skill points to specific effects, and gains a +2 synergy bonus on any effect that changes no more than one variable from the original effect, provided his skill in the effect is 6 or higher. Also, a Psicraft rating of 13 or higher allows a +2 synergy bonus on all effects.

Skill points at 1st level: (2 + Int modifier) * 4
Skill point at each additional level: 2 + Int modifier

Saves: Fortitude (poor), Relfex (poor), Will (good)
Attack Bonus: As Wizard

Weapon and Armor Proficiency: Psionicists are proficient in all simple weapons and light armors. However, the armor check penalty always applies to their psionic effects, and is doubled if the psionicist wears a helmet. These same penalties also apply to wild talents. All the other penalties and restrictions on armor use are standard.

Feats: At first level, a psionicist gains four bonus feats. The first is Mental Combat, a necessary feat for anyone who wishes to defend themselves from mental combat. The other three must be used to select psionic Areas of Control from the new "Psionic" category of feats. For every three class levels after 1st (at 4th, 7th, 10th, 13th, 16th, and 19th), they gain an additional feat from this category. These feats may be taken more than once; each time they are taken after the first, they add a +1 Area of Control bonus to every effect that uses them. Note, however, that Area of Control bonuses may never exceed 5.
Note that psionicists are unable to use any standard feats from the Item Creation or Metamagic categories, unless they also belong to a spell-casting class. Most of the Metamagic feats can be duplicated by a psionicist willing to increase the cost of his effect, and the Item creation feats are beyond the reach of all non-spellcasters. Combat Casting, on the other hand, is very useful to them.

Areas of Control: Since each psionic learns his powers in a different way, every psionic will have different areas of control. Some, having been raised in a magical society, will give their Areas of Control pseudo-magical names; Pyromancy, Divination, Healing. Others will name them based on their own personal system, or use "sophisticated" sounding-names like "Psychometabolism" or "Psychokinesis". In general, there will be 5-9 Areas of Control that any given psionicist can learn according to his own personal system; consult your DM as to what he considers reasonable breadth for Areas of Control.

Psionics: A first level psionicist has Psionic Strength Points (PSP's) equal to his Intelligence, Wisdom, and Charisma combined, plus any Area of Control Bonuses. At each additional level, points gained equal the psionicists current Int, Wis, and Cha bonuses, plus any Area of Control Bonuses (but always at least 3 points per level). Points are regained at a rate of 0 per hour in heavy exertion, class level + Wisdom bonus (minimum 1) per hour at light exertion, class level + (2+Wisdom Bonus) per hour with rest (at least 2), or class level + (4+Wisdom Bonus) with an hour of sleep or meditation (at least 4 per hour, though). Wild talents, obviously, do not have a psionicist level to add, so must use the base number.

Each psionic effect has a difficulty based on five factors: How long the psionicist is willing to concentrate, how far away they want the effect to happen, how long they want it to last, what area they want it to affect, and what the effect actually does. Sometimes, the last category will be irrelevant (as determined by the DM). In that case, the category is ignored. The difficulties of these five effects are added together, any Area of Control Bonuses are subtracted, and that is the PSP cost, as well as the Difficulty Class of the effect. If an opponent strikes the psionicist while during the concentration time, the effect level is added to 15 to determine the difficulty of the Concentration roll.
In order for an effect to work, a psionicist must roll a d20 + Attribute Bonus + Skill Bonus (if any) + 1 at psionicist levels 1, 5, 10, 15 and 20. You may not Take 10 or Take 20 with psionic effects; while the will can be tamed, it is not a task without stress. At the start of a psionicist's career, he must choose which attribute (from amongst Intelligence, Wisdom, and Charisma) will provide the bonus to his powers. This selection may not be changed later. If the roll fails, one half the effect cost is still spent. He may try again, but each failure adds 1 to the PSP cost and Difficulty class.
If a save can be made, it must beat the psionicist's effect total to be successful. A successful save means that the effect is completely unsuccessful; no damage is inflicted, no information is gained, but the PSPs are still spent. An unsuccessful save means that the effect works as usual. The type of save is determined by how the effect is to happen. Creating a bolt of force that flies towards the target will be resisted by a Reflex save to get out of the way. Delving into someone's mind for information can be resisted by a Will save, and an attempt to age someone will be resisted by Fortitude.

Concentration Time (Point cost)
20 minutes (1)
10 Minutes (2)
1 minute (3)
1 Round (4)
1 Action (5)

Note that, if a Concentration roll is required, the DC is equal to the PSP Cost of the effect being attempted. An effect may be Quickened so it may be gotten off with no concentration whatsoever, but that is worth 10 effect points.

Range (Point Cost)
Personal (1)
Touch (2)
Close (3)
Medium (4)
Long (5)

These ranges are identical to the ranges for spells listed on page 148 of the Player's Handbook.

Duration (Point Cost)
Instant\1 round (1)
1 minute (2)
10 minutes (3)
30 minutes (4)
1 hour (5)

No effect the creates or heavily modifies an object can use the "Instant\1 round" category to become permanent. Effects that return something to its original condition (such as effects designed to heal), destroy something, or create a medium of attack (such as fire) may have a duration of instant. Effects that enhance abilities, change shapes, or create a physical object will have a duration of 1 round instead of instant. For effects with any duration longer than instant (be it one round or one hour), the effect may be extended by expending the duration point cost again, without an additional effect roll being made.

Area of Effect (Point Cost)
Individual (1)
10' radius (2)
20' radius(3)
40' radius (4)
50' Radius (5)

Note that if the psionicist only wants to affect certain creatures within an area of effect, he must pay the Individual cost for each one, rather than the generally cheaper radius-based effects. Radius-based effects will force everyone in the area to make a saving throw.

Divination effects designed to see the past or future have an additional area of effect (they still require the normal area of effect to choose who or what they want to see the past or future of). Rather than affecting a target, they see to a section of time. Since the future is harder to see than the past, its times are generally much shorter (and are listed second below). To see beyond one decade, effects cost one additional point per extra decade.

Viewed Period (point cost)
1 day / 1 round (1)
1 week / 1 minute (2)
1 month / 10 minutes (3)
1 year / 30 minutes (4)
1 decade / 1 hour (5)

Lastly, there are actual effects. Two general types of effects are accounted for: Damaging/healing effects and Bonus\General effects. Damage/Healing effects either take away or add a number of Hit Points to the target. With damage, it may ignore hardness, depending on how it is inflicted. For example, a Geomancy effect used to disintegrate a rock will ignore hardness, since the rock is essentially just crumbling. If the Geomancer instead opted to bash that rock with another, then hardness would not be ignored. In the end, it is up to the DM to decide.

Damage\Healing (Point Cost)
1 Point/level (1)
d2 per level (2)
d3 per level (3)
d4 per level (4)
d6 per level (5)

In the case of Bonus and general effects, each point of bonus or minus costs one point. A bonus from an effect can be added to a skill (though not another effect), an attribute, used to enhance weapon damage or armor absorption, or to a saving throw or attack bonus. A minus can be used to do the opposite. Other effects must be adjudicated by the DM, but generally one can be improvised by judging how much it would be worth, if it were a penalty. For example, an effect that caused or cure blindness would be about 4 points, since the target would be gaining/losing a 2 point reduction on both AC and attack rolls. One that changed a character's into a tiger, however, would be worth at 5 points, as his body would be undergoing some major changes (and the psionicist would need to pay for any attribute differences to make his tiger very convincing). On the lower end, an effect that summoned a small fly to buzz around an opponent would only be worth 1 point, since it would be only a minor distraction, while a teleportation effect would ignore this category all together, since all that needed to be determined is who's going and how far.

Mental Combat: Because of their versatility, it is quite dangerous to have a psionicist on the opposing side of a battle. As such, psionicists have developed methods for taking each other off the field. These attacks happen beyond the reach of normal minds, and so non-psionics cannot be affected by these. Wild talents, on the other hand, are completely vulnerable until they recieve training in psychic combat (and have taken the feat).
Mental combat takes place much like physical combat. To engage in mental combat, a psionicist must make a mental image of himself, called a construct. This construct is the psionicist's form for both attack and defense. Regardless of the appearance, however, a psionicist's construct always has the same abilities, though a particularly apt construct might gain a +2 bonus against another; for example, a griffin constuct will gain a bonus against horse construct, or a construct of St. George would gain a bonus against a Dragon construct). If a psionicist finds himself in a bad situation, he make take an action to alter his construct to something more suited. This can often turn into a battle of shifting shapes as much as actual damage.
Every psionicist has a base Mental Defense of 10 + Intelligence Modifier, with an additional +1 at levels 5, 10, 15, and 20. Their Intelligence modifier also adds to their initiative. Their Mental Attack Bonus is equal to that of an unarmed monk of the same level, plus their Charisma modifier (thus, a 6th level psionicist with a 17 Charisma will have a +7 on his first mental attack of the round, and a +4 on his second). Damage and criticals are rolled as if the psionicist were a medium-sized monk of equal level (with a damage bonus equal to the psionicist's Charisma modifier, and a damage penalty based on the target's Wisdom modifier), but is treated specially. Rather than doing real damage to Hit Points, any damage from mental combat is treated as subdual damage to the opponent's PSP's. As with subdual damage, once the damage inflicted equals or exceeds the target's PSP's, the target is staggered or unconscious. The temporary damage from mental combat heals at the rate of 1 point per character level per hour, and recovery from unconsciousness is identical to that from subdual damage (see page 135 of the Player's Handbook for details).
A wild talent who engages in mental combat is treated similarly. However, Their Mental Defense is only 10 + Intelligence Modifier, their attack bonus is only their Charisma modifier, and they do only 1d6 + Charisma Modifier - opponent's Wisdom modifier damage. If someone who is not trained in mental combat is engaged in mental combat, they do not get a construct (their mental form is simply a ball of light), and have a Mental Defense of 10 + Intelligence modifier. If they try to make an attack, they attack with a -4 and provoke a mental attack of opprotunity from a trained combatant.
With such potentially severe consequences, many psionicists wish to avoid mental combat. There are several ways to do this. First of all, all psionic combat is line-of-sight. If you opponent can not see you to initiate the combat, you cannot be engaged. Once engaged, a character may also attempt to break free from combat. A character may make a Will save in order to escape combat. If his opponent wishes to keep him in the combat, he may also make a Will save. If the escaping character's total is higher, he has broken free from the mental combat and may not be engaged in mental combat by that opponent for one minute. If the attacking character's total is higher, he gains a mental attack of opprotunity against the escaping character and the combat continues. If the two totals are equal, both results happen; the escaping character manages to disengage from combat, but his attacker gains a mental attack of opprotunity on him. Note that if the combat has more than one opponent, it is possible for a character to disengage from one, but not from another; each person who is unwilling to let him leave combat may make a Will save in order to force him to stay, and his total must be higher than each of them. Lastly, certain magical items (such as a Ring of Mind Shielding) make a character completely unable to engage in mental combat.

Psychic Supreme (known to the bards as "The Modest") has straight 18's in his important stats at 4th level, and has put one feat each into Telepathy, Psychokinesis, Clairsentience, and Psychometabolism. This means that he had 53 PSPs at 1st level (when his Charisma was only 17), and gained 11 PSPs at levels 2 and 3, and 12 more at 4 (when his Charisma went up to 18). He has, at maximum, 87 PSPs. His powers are all based off his Intelligence stat (which he intends to increase at every available opprotunity from now on). He also has 17 Hit Points, and a +1 ability bonus from his other stats.

When the group settles down for the night, he starts the fire using Psychokinesis. He wants to do it quickly, so he spends only one round in concentration. The range is touch (since he's within arm's reach of the firewood), the duration is instant, area of effect is personal, and the effect is 1 point of fire damage. This gives him a total effect cost of 9. With his attribute bonus of +4, and his level bonus of +1, he needs only to roll a 4 or better to create the desired effect. Since the wood is inanimate, it gets no save. The fire is started easily, and is down to 78 PSPs.

Suddenly, from out of the woods, a group of goblins attack! His allies quickly move into hand to hand, so he can't drop the fireball he intended, so he instead opts to smash one with a bolt of pure force. He does this quickly, with only one action's concentration, at medium range, and for only an instant. Since he's only hitting one, the Area of Effect is individual, and the damage is a d6 per level (4d6). The total is 5+4+1+1+5, or 16. His bonuses are still +5 to the effect, and his roll of 11 barely succeeds. The Goblin he attacks rolls a Reflex save, since this is something he can dodge, and comes up with a 17, meaning the blast misses the goblin.

Eventually, the goblins are beaten. Psychic Supreme wants to find out where the come from, so he uses a Clairsentient effect to look back over the Goblin's past day. He concentrates for 20 minutes, touches the goblin, and gives himself 30 minutes to look through the day. Since it is only one goblin, and the effect is covered by knowing how far back he looks, his total is 1+2+4+1+1, or 9. Another simple effect, and he flubs it royally, spending 4 points (9 divided by 2, rounding down). He tries again, with a difficulty and cost of 10, and makes it. He sees a human, somewhat vague in the image, commanding the goblins to go out after his group, as well as several shadowy shapes in the background.

So far this evening, Psychic Supreme has spent 39 PSPs, leaving him at 48 PSPs. He and his group set up watches, meaning Psychic Supreme gets 8 hours of sleep and 2 hours of rest (nothing happened on his watch) in which to regain PSPs. Since he is 4th level and has a 18 Wisdom, he would usually get back 32 (8 hours * his class level) + 128 (8 hours * 4 Wisdom bonus) + 8 (2 hours of rest * class level) + 12 (2 hours * 2 + wisdom bonus) PSPs, or 180 PSPs. Since his maximum is well below that, he's up to maximum in the morning.

The group sets out after this mysterious man who sent the goblins to kill them. After about an hour of travel, they come to a cave like the one Psychic Supreme saw in his vision. A troop of bugbears comes out of the cave, followed closely by the man from P.S.'s vision. The battle is on, with P.S.'s friends fighting hard against the bugbears, and P.S. brought into psychic combat against this strange man.

Psychic Supreme appears on the mental battlefield as he usually does, as a huge man, rippling with muscles, clad in shining plate mail and armed with a huge sword... Psychic Supreme's own mental image of himself. Across from him is a man wearing demonically styled full plate, and bearing a jagged axe... his enemy's dark visage.

Psychic Supreme has an attack bonus of +7... 3 for his level, and 4 more for his Charisma. His Mental Defense is 14, because of his high intelligence, and he does 1d8+4 damage on all attacks, and subtracts 4 from all damage done to him. His PSPs are 87, as he hasn't spent any, yet. Unknown to him, his opponent has a +7/+4 (6th level with a 17 charisma), a Mental Defense of 14 (17 Intelligence, plus level modifier), does 1d8+3 damage on all attacks, but only subtracts 1 from all damage. His opponent has 81 PSPs.

In the mindscape, they are instantly upon each other. Psychic Supreme, thanks to his superior intelligence, goes first (both managed to roll a 10 for initiative). His attack is a 20, which produces a threat, followed by a 14, which is enough for his first strike to cause 2d8+8 damage. He rolls a 5 and a 2, meaning he does 15 points of damage! His opponent's Wisdom means that the damage is knocked down to 14, however. His opponent, however, then gets to make a full attack, getting a 16+7 (23 total) on the first attack, and a 10 total on the second. The damage from the first attack (the only one to land) is a mere 5, which P.S. all but ignores (takes only 1).

Next round, P.S. attacks, while his opponent refocuses. P.S.'s attack roll is only a 7, but that's enough for a hit, and he does another 8 points of damage. So far, his opponent has taken 22 points of damage, but his opponent goes first on the third round.

Again, his opponent makes the first attack, but flubs the second, meaning he does 3 points of damage once adjusted for P.S.'s Wisdom. P.S. strikes again, and does another 9 points of damage, bringing the total up to 31.

His opponent has had enough, and thinks himself vastly overmatched. He tries to flee the mental combat, rolling a total of 16 on his Will save. P.S. wants to keep him in the combat, and rolls a 22 total. His opponent is forced back into the combat, and takes 7 points from P.S.'s mental attack of opprotunity, and another 8 from Psychic Supreme's actual attack. The total is now 46 mental subdual damage to the enemy psionicist, and 4 for Psychic Supreme.

On the next round, the opponent wrenches his mind free from Psychic Supreme's (a 22 total vs. P.S.'s measly 14), to find his bugbears still locked in combat with P.S.'s friends. Both Psychic Supreme and the enemy psionicist now roll initiative for the normal combat, as they've been involved elsewhere for this time. The evil psionicist, fearing for his life, uses his Pyrokinesis Area of Control to summon up a wall of flame. The effect cost is 19, and the wall roars up. Since he's now spent actual PSPs, we see that he has 81 - 19, or 62 PSPs, but since he's taken damage from Mental Combat, he can only spend 62 (his actual PSPs) - 46 (the mental subdual damage) or 16 PSPs before he's staggered, and trying to spend 17 will knock him out. Psychic Supreme uses Psychometabolism to increase his capability to jump. He decides that he wants a +12 bonus to his Jump Skill so he can get over the 8' wall of fire, and his effect cost comes out to be 20! With a +4 for Intelligence and a +1 for level, P.S. will be hard pressed to get this bonus, but he luckily rolls an 18 and just makes it. He takes a running jump at the wall of fire and comes out with a total of 29 on his jump skill, meaning he only manages to clear 6 feet, and passes right through the wall of fire. The wall does 6d6 damage, and rolls a 17 (which will normally put Psychic Supreme at 0 HP), and P.S.'s Reflex save of 14 doesn't help him any. Psychic Supreme drops to the ground on the other side of the wall of fire, smoking slightly and fighting for consciousness as his opponent advances on him for the coup de grace...