Spitfish just recently launched their PS3 mouse that is compatible with PC and Macs, but have now launched their mouse controller for the Xbox 360. It includes XYAB buttons that the Xbox 360 obviously has and places them right near your thumb. On the nun chuck, there's a d-pad, analogue stick and trigger buttons.
The setup works wirelessly through the USB dongle, and sports lag-free gameplay, is customisable, and lasts up to 50 hours on just two AA batteries. Spitfish say the mouse is the "world's first super precision mouse hybrid gaming controller for the Xbox 360". The PS3 version is available in the US for US$90.