A new version of iDoom has been released a couple of days ago. The new version features support for Apple's iPod nano and has configurable controls.
iDoom is a port of the classic id game Doom to the iPodlinux platform. It is based on the sourcecode from the original doom released by John Carmac in 1997.You can get it here.
iDoom currently supports all iPod-versions that can run iPodlinux.