Depends on what you like. Real Racing on the iPhone is awesome, if you like racing sims (it's not an arcade-racer, for that you want something like Need for Speed). Geometry Wars should be good, it's based on an Xbox 360 overhead space shooter, you play it like Smash TV or Robotron, with one control stick to move, the other to shoot. For a card game to fill in short gaps of time, I've been a real fan of Dungeon Solitaire - it's a mix between CCG's like Magic: The Gathering and Solitaire, and it just got an iPad update. X-Plane is a great flight simulator on iPod, the iPad version sounds like the ultimate version of that. Zen Bound is a fun game that's a very physical puzzle game, where you rotate a model in all axes trying to wrap a rope around as much surface-area as possible. Flight Control is a fun game where you are guiding planes and helicopters around to land at airports without running into each other - it can get kinda frantic with lots of planes in the air. Field Runners is a classic iPhone tower-defense game, Civilization: Revolution is a good strategy game. Speaking of which, Galcon is a very fast-paced realtime strategy game designed specifically for touchscreens and multitouch, while Command and Conquer should be a good standard RTS.