I'm not the sort of person who would actually recommend playing a game, but for perhaps once in my life, this game is worth checking out. It's called Cube Runner, a free download from the App Store for iPhone and iPod touch version 2.0. Simple, fun, challenging and has much replay value!
The video below shows you what the game is all about:
As you can see, the App Store has transformed the iPod touch into more than just a multimedia player. Increasingly, it is becoming a viable gaming platform too, with it's unique combination of accelerometer and touch-screen interface.