By "classic" games, do you mean classic arcade? Did you look in the
Emulator subforum here on Mobilitysite and
Menneisyys's arcade emulation guide? The best arcade emulator
PocketCultMAME runs on PPC 2003. Play all your favorites like Centipede, Zaxxon, and Scramble (among many others).
As for standalone arcade games, have you looked at the software stores here at
Mobilitysite and
Mobihand? As for recommendations, there's only one game I still play even after 2 years and that's Skyforce Reloaded (top-down shooter). Hope this helps :-).