When Wizards of the Coast moved Dungeons and Dragons from version 3.5 to 4th Edition the licensing of 3rd edition 3rd party products went away. For Green Ronin, the solution they came up with was to rebrand those old products as '3rd Era' and re-release them as PDF documents. One of the first I've seen advertised was 'The Psychic's Handbook', an alternate set of Psionics Rules for D&D. Seeing this come through put me in mind of psionics in general. I've always been a fan and if I play another D&D game (unlikely right now) I will definitely lobby to play a psion or related class.

It's probably worth noting that Green Ronin's Psychic's Handbook is more or less the baseline of what became the magic system in Green Ronin's Blue Rose/True20. It is a somewhat free form skills and feats based system though it is lighter on the skills and feats requirement than some of the other ones out there(see below) and it is a very big gap between that and what psionics in D&D have been.

Psionics was introduced to the original Dungeons & Dragons game in Eldritch Wizardry, along with Druids. The system then was something of a tradeoff by class. If you were a fighter there were a certain number of psionic related fighter abilities that could be attained at the expense of some of the standard fighter abilities.. or possibly an XP penalty (those were popular back then).

By 1e the Psionics system was basically a roll to see if you've won the lottery sort of thing. All of it was completely random and your chances improved slightly for having high mental traits (like going from 1% chance to 3% chance). You got essentially a 1/day-ish power that was likely to be something like 'walk on quicksand' or astral projection and basically became a magnet for a thousand and 1 critters who wanted to suck on your brain. It was like a giant bullseye.

2e kept the roll for a 1/day power and introduced a class that gets a bunch of those powers. The powers were 2e skill (non-weapon profieceny) based. So a telepathy power might be Int-3 with a roll under mechanic to get it to work. Roll exactly the target number and you get a bonus. Roll a (1 or a 20 I forget) and you fry your brain or another power specific penalty. The power level was such that you could get really powerful effects early with the suicide level intended as a balance.

Skills and Feats Psionics Systems seem to be intuitively how people want psionics to work in d20. There is the Psychic's Handbook, Ken Hood's system (along with a similar and linked Martial arts system), Craft of the Mind (which takes its cues from Star Wars D20), and probably a few others. The psychic's handbook has the benefit of being a published book and having a number of customizable items in the back. For a game I was running, I would use the base system to make psionics less powerful than Magic but also more common. Having it be feat/skill, its fairly easy to give any old fighter at least one psionic trick that he can use every so often. If it gets abused, there is always the option of adding in one of the limiters like a fatique save or ability damage.

Oh psionics, I love you so.