Nightfall said:
Ritual Magic in Relics and Rituals.
True Rituals.
Ritual Casting.
That's a good start.
Psionic augmentation.
Take 10 / Take 20.
Templates in general. These date back to 1e, but they get formalized and put to good use.
Spycraft action dice.
The UA action point feat emulation mechanic. All the sudden, every feat resource you have is a "book of stunts".
Mindscapes psionic combat in Hyperconscious. Finally, psionic combat that works and is easy to use.
Spell slots. There, I said it. Gygax's classic mechanic proves itself easy to use, and very effective at both letting wizards strut their stuff and limiting their capabilities.
Spycraft 2.0's use of wisdom for reserve items and charisma for gear picks. Dump stat this, baby!
Soul Magic in Book of Eldritch Might III. Devious. Fun.
Paragon Classes/Racial levels. Get out the dark ages, LA's!
Disadvantages/Backgrounds as seen in games like Spycraft 2.0, nWoD, weapons of the gods, Haven d20, and 7th Sea. No more point farms for players who never intend to live up to their disads!
That's a good start.