There as been plenty of discussions on helmet camera for the extreme sports crowd but one sticking point is low light and night action.
For our work for outdoor sports we have been running the Adrenaline Sytems Ghost Cam II which has a day and night function. It produces great images and allows for maximum quality using a good Camcorder or DVR (of course)
They also have varifocals and a wide variety of mounts.
Our group has been using their stuff and have been happy with their help in this difficult field of extreme shots.