Freetar is a Free open-source game based on the gameplay set forth in the hit Playstation 2 game 'Guitar Hero'. It supports a large variety of gamepad configurations (as well as the Guitar Hero controller with a Playstation -> USB adapter).
The Freetar Editor is a closely related project that allows users to create songs for Freetar from songs on their computers - allowing a near unlimited number of songs.
The official Freetar Homepage is http://www.freetar.net/ - check out the 'Songs' forum for a list of songs that people have completed. The manual for the Freetar Project is available online at http://www.freetar.net/wiki/