Audio Surf is a Windows game that makes completely unique levels for the user. Using music on the players computer it analyzes it and creates the track accordingly giving it endless possibilities. It would however only work using iPhone OS 3.0 as it would need access to the users iPod Music and using the improved graphics chip, could give some amazing graphics.
To control the game you would tilt the device, using the accelerometer to control the ship. You could challenge friends using the notification system and submit scores to online leadboards. This game would work great on the new iPhone OS, just hope someone makes it.