Just wanted to point out that most standard camcorders do very well as on-board cameras. A decent camcoreder in the $ 300 range is more expensive than the little helmet-bike cameras, but the picture quality and recording length are far superior.
Also, most newer digital still cameras such as Sony Cybershots also take MP-4 movies but the recording length is limited by the size of the memory card.. not a big factor if you shoot selectively.
To attach either camera to your rail, you can get a tripod mount which hose-clamps to your tubes with rubber back from:
http://www.cyclegadgets.com/Products/RAM/r...prod=RAM-CAMERANote you have to select the parts to build your specifi application - you need the base, an extension, and the tripod mount.
RAM makes hundreds of mounts for GPS units etc but for any camera with a tripod socket you dont need a specific mount, just the camera set up, then later you can add GPS holders, iPod holders etc