Atomik Psionics is probably the best generic reading material. Like
GURPS Powers and the old GURPS Psionics, of the Hero system (naming
two), this supplement gives many frames to hang PSI onto (quantum
physics for hard-SF, alternate dimensions to include magic as a
companion). Whereas Hero breaks PSI down into the specific effects so
the player can combined multiple effects to create anything (ground up), Atomik and GURPS uses broad-based power attributes (or power levels in GURPS 3e) and skills to simulate fiction and the movies. All are good.
Atomik is additional, and exceptional, reading.
<br><br><b>QUALITY</b>: Excellent<br><br><b>VALUE</b>: Very Satisfied<br>
[4 of 5 Stars!]