I have seen a couple of camera mounts pictured and explained on BF. Here's my (well, not entirely mine) simple version. It uses stuff we all have in those coffee cans out in the garage. It starts with a U-shaped pipe holder, a small piece of metal (aluminum in this case) with a couple of holes drilled in it and two bolts, one of which fits the tripod mount on a camera. When I find one, I will put a second wing-nut on the rear bolt, too. I added a little padding between the camera and the piece metal. You may recognize it as an extra helmet pad.
I have used it to take little 3 minute movies with my digital camera in movie-mode, but it can be used for stills, too. The movies won't win any academy awards, but they are fun to look at. So far, we've been doing downhills. It helps to have a couple of people riding in front of you. This weekend we have a club ride with lots of people. My camera happens to be a Canon Power Shot S1 IS, but, of course, any camera will do, including a movie camera of some sort.