In another thread, someone asked about types of cameras available (after nearly being struck by an aggressive driver but had no proof to take to the police). I selected my camera specifically for this purpose:

http://www.chinavasion.com/sports-action-camcorders/cvsadv52/

This unit has a bullet camera that is mounted in my helmet and I stick the DVR unit in my front jacket pocket or side pocket of my backpack. What I like about it is the ability to add a 16 GB SD card for memory (I can record hours of video), the automatic video 'loop' feature (overwrites oldest videos if the memory card fills), the two-hour battery life, and the ability to purchase additional batteries that can be easily swapped out. This unit also comes with all kinds of different mounts and AV cables for recording and playback. My only complaint so far is that the video contrast/quality is low and the cord to the camera is a bit cheap (I already have a loose connection after 4 months of use). Price is very good though.

For the same money, another great option is the Looxcie cam. Another user here has one (ride) and has posted video of it in action. The video quality is noticeably better, although you wear this camera and the battery options are not as good. If I were to buy another unit, however, I would probably go with this one.

I think some one else here has a GoPro camera, which is another population option. Chime in with a description if you feel inclined to share your thoughts.