Marathon would be a great game to port. It was the game Bungie made before the famous Halo series. It looks like an updated version of the Doom game. The source code is under the GPL, and the game content is free (non-GPL, though). That really should not be a problem. Even better, the source code is already based on SDL!
http://trilogyrelease.bungie.org/
I've ordered my GP2X, and counting the ceiling tiles 'till it comes.
http://trilogyrelease.bungie.org/
I've ordered my GP2X, and counting the ceiling tiles 'till it comes.