While we expect to see some great iPhone games once the SDK is launched, there are still some developers working on unofficial Jailbroken games. A particularly impressive example of this is a port of Kenta Cho's Noiz2sa.
The game is a vertical shooter. The objectives are simple: Avoid the bullets, kill the enemies. The game was ported by Lazrhog and an early version is available to Jailbroken iPhones via the iPodTouchFans repository.
The developer is also working on an OpenGL ES version with multi-touch support which is shown as a preview here:
The most recent version does not appear to be publicly available. While we certainly hope we might eventually see this become available through the iTunes App Store, there don't appear to be any plans at this time.