One of my favourite flash games is Cubefield, the objective of the game is to get you through a field of cubes that are dynamically created as you play the game. I’ve thought for a long time now how good this would be as an iPhone app using the in-built accelerometers and put together a mock-up to demonstrate what it would look like.
As you can see it would work perfectly on iPhone and iPod Touch using the in-built accelerometers.
Update: It seems it already exsists in the App Store under Cube Runner.
Sam's Blog 
Awesome game. The game actually already exists as a free application in the app store. Search for “Cube Runner”