3G and GPS in the same unit.
Everything else that everyone wants, I believe is software updatable so I would only buy a new iPhone if: 3G and GPS were included in the same unit. I would NOT buy a new one if ONLY 3G or GPS was in there.
I would buy a new one with GPS, but I also need a louder maximum volume-- I never hear the thing ring in my bag. The international plans should less expensive too-- I also want to be able to use music I own as a ring tone.