The best would be to get a proper bullet/lipstick cam and have it attached to a camera in your back pack via AV cables, or attached to a hard drive. My mate found a cheap webcam that took reasonable quality which he could hook up to a camera in his back pack. However if you want to be like the rest of us use a lot of tape and a video camera, it's as simpe as that.

The best 'dodgy' rig I saw was someopne at our local who made their own look back boom rig. This segment from Drift 3 shows one being used
http://www.youtube.com/watch?v=xcD0sisR6tE

The guy at the track rigged one up by tabing a camera to the end of a broomstick, then with immense amounts of tape and two bolts he stuck it to his helmet and then had a brick on the other side to counter balance the weight. With this rig you have to be careful of trees ahead of you and if you crash you will probably stuff up your neck, so don't ride 100% with it.