Firmware

http://code.google.com/p/procfw/

Some games to test:

Scummvm

http://wiki.scummvm.org/index.php/PlayStation_Portable

Games for Scummvm 

http://scummvm.org/downloads/

GBA Emulator http://psp.scenebeta.com/noticia/unofficial-gpsp-kai

Roms for the GBA emulators

http://bitbin.it/oJvvkjrh