Attack of the 50ft Robot!, developed by students at DigiPen Institute of Technology, is great example of well-formed indie title. Game takes place in 1950s B-movies style setting, spiced with black-and-white old projector postfilter. Chased by tanks, helicopter und ufos, Giant Robot, controlled by player, grinds whole city in return.
Fast every building can be smash to pieces, and massive-scale rigid body dynamics is handled by PhysX SDK.
You can download Attack of the 50ft Robot! here (158 mb)