ARDefender is a Augmented Reality game that seems to be a load of fun.
It is a marker based camera view game. The target is to destroy an army that attacks a tower which you control using your iPhone.
Have a look at the gameplay in the movie.
Students have made a 3D mobile AR game with the help of Nvidia hardware. The game can be played by moving your mobile device over a game zone which has been outlied on a table.
I will see people playing these types of first-person shooters with the new iPhone 3G S (“S” as in Steve ;) ) real soon because of the OpenGS hardware rendering real soon.
Take a look at the video