Created by Marco Giorgini - this is one of the better first person shooter (FPS) games available currently for the iPhone.  The game is reminiscent of the original Doom or Quake and plays/looks really nice. When playing you can use the accelerometer to move around which is really cool or you can get a little touchpad which makes it a bit easier at first.  Definitely try the accelerometer though since you have one in your iPhone and iTouch.

The key to getting this game is you must jailbreak the phone/ipod and then use the installer.app to actually install it.  If you're nervous about jailbreaking the phone definitely read the instructions through and backup first.