There are many sites that review about free iPhone games, particularly i wanna cite the following nice resources that allows you to stay updated and download new iPhone free games:
OpenFeint Game Spotlight free app available on the store that allows to access to the best free games, producer site
FAAD free app day, get a free game everyday!
FreeAppReport web site that regularly review free games
ifun 4 free iPhone optimized web site with many free games, divided by categories too