http://www.naturalpoint.com/trackir/
Guy from work had this delivered today. Which is an Infared motion tracker for a hat or headphones. It lets you use your head movements to control where you look, rather than moving your body in the game. This is about as geeky and cool as you can get all at the same time. I couldn't find the video on Armed Assault we watched at work, but the game tracked the users EXACT head movements (it was pretty cool... maybe almost wii like application) so, you can see someone nodding or indicating no IN GAME... It is somewhat like free mouselook, but not really. This is just kinda cool I think.
This is the lowdown and looks really cool on Armed Assault.
http://www.youtube.com/watch?v=_AO0F5sLdVM