What about pocketSCUMM? Or is does that not qualify as a RPG? More of an adventue I guess. I like it a lot, allows you to play old lucasart games like LOOM and Monkey Island. Nice graphics, and these games are very playable on the ppc screen.
link:
http://arisme.free.fr/PocketScumm/
Edit: The classic "Beneath a Steel Sky" is now available as freeware! Check the link above. For other games you need the roms. Lots of people will have copies of these games lying around somewhere (Ihad).