Yeah, I've messed around with quite a few setups over the years.
You can mount
a Camcorder onto the bars, etc, a tape version will offer the best security for the recordings, the disc type used to be unable to write to the disc, not sure if they are better nowadays. I think these offer the best picture quality. These can be the cheapest solutions.
A bullet camera
can be had for around £150 and be hooked up to a camcorder, the camcorder must have an AV in
, not sure that the newer one's on the market have this. You will need a power supply for the bullet camera and a LANC controller for starting and stopping the recording, and the bullet cams have a smaller CCD resolution so the picture quality is not as good as a camcorder.
Then there are the digital recorders on the market, the advantage is that you can just copy the footage in file manager whereas with DV Tape you have to replay it onto a PC. I personally don't like MP4 quality so use MPEG2 devices (same quality as DV Tape). Hard Disk recorders can break, my Archos unit did, so solid state devices mean the footage is safe and be transfered easily.
I currently run a Chase Cam PDR and bullet cam, the PDR is powered via the accesory socket and the camera via the PDR a LANC is connected to start stop recording.