NaturalPoint has developed a new version of their TrackIR head tracking system that links your actual movement to the in-game view, allowing you to look around in virtual worlds just by turning your head.
The new TrackIR 5 has been improved in many ways, including 10 times the resolution of TrackIR 4, a wider field of view, improved ambient light filtering and 120fps sampling rate. TrackIR 5 is compatible to all major racing titles, including rFactor, the Simbin simulations and iRacing.
The system sells for $149.99, more info and the official store can be found on the NaturalPoint homepage.