id Software have launched Wolfenstein 3D for the iPhone. It is available now from the App Store. John Carmack himself has been working on porting it over to the iPhone.
Although Wolfenstein 3D isn't one of the most modern games available (it was one of the first FPS games) it still fits perfectly on the iPhone. It's ease of play and challenging tasks will bring back memories to all who download this game. Also, it only takes up a couple of megs in space.
Other good news is that id Software are working on Doom for the iPhone too. With the original creators porting these games over you can expect them to run exceptionally well.
Also check out details of how the project came together over here.
If you like 3D stuff then check out this cool 3D cube.