Well, the SRD has spell points, which are basically just porting the 3.5 psi rules back to normal casters. Elements of Magic is a fairly well-known third-party point-buy casting system for d20, but it's also a bit too complex for me. It permits making up spells on the fly during combat, and has a huge number of potential effects that it can generate. True Sorcery's similar; it effectively runs on a point system (either via subdual damage or a 'casting buffer' of mana points), and allows for spell creation on the fly, but is likewise pretty complex. I find it math-heavier than EoM, but it's skill-based and there are fewer spell seeds so it's easier for me to manage. The Iron Heroes spellcaster class was point-based, but would be hard to backport to normal 3.5. I've also played with a few fanbrew point-casting systems over the years, but there were all quite broken and I'm unable to locate them.
As far as comparisons go between d20 spellpoint rules go, honestly 3.5 Psi / spell-points is the simplest I've played with, and probably the most balanced as well. If you're looking at a stamina-based model, though, I recommend considering True Sorcery; it appears to be similar to what you're seeking. It can also be made simpler in play by creating a list of spells with DCs beforehand, rather than permitting on-the-fly creation. d20 Warheart's magic, while not point-based, is also skill based (but would require significant backporting).
