oregon scientific has an "extreme sports" cam that mounts on a helmet pretty easily. we used them a few times in Afghanistan.
also, I made a rail mount for a camera- pretty simple: basically a tripod top on a section of rail clamp. I would mount it on the side of my M4 with a small digital camera attached. worked pretty good, just had to rotate the video 90 degrees to watch it.
oh, use a cheaper camera. they break