I resently stumbled accross the source code for this excellent FPS game called Marathon by Bungie (you know, the guys who made halo and halo 2). Marathon was originaly for the Mac but it has been ported over to Windows. I'm wondering if anyone looking for source codes to port to the PSP may want to take interest in porting this game.
For more info on the source code and game check out http://source.bungie.org