Eye Tracker Mouse
TrackIr 5 Optical Head Tracking System
This one is mostly gamers playing flight simulator games. It is not a mouse substitute, but supplement.
Lots positive reviews on amazon.
SmartNav Natural Point Hands Free Mouse
You wear a headlamp-like thing to your head, it shoots a lazer pointer, and the screen detects the pointer. So, basically you just move your head slightly to move pointer.