Among all the webcam based head tracking solution, I found this one really interested. A new software solution offered at cachya.com. It has 6DOF output and pretty good performance. I used it with my 3 years old webcam, works just fine. Even with a relatively low frame rate (23fps in my case), cursor response is very much smooth and fairly fast, especially when the double rate is enabled. According to their website, it 'predict' rather than merely 'detect'. Sounds to be a good idea.
It simulates a virtual joystick, so may potentially work with most of new games. It took me some time to figure out how to deal with game configuration, but once it works it works great. Have tried in Lock On and Aces High. Targeting for Armd Assult.