I use the IOPort camera mount on my harness bar. Works very well. I also tape a bullet cam on/in my car for different views. Duct tape also works well. Here's a pic of the camera on the harness bar with a bullet cam on top the car.
As for camera, just get something reasonably modern, and digital, with Firewire at least for getting the video onto your computer. Expensive cameras can get you better optics and also better performance in high, low, and normal lighting conditions.
Try to get a camera that has an A/V in/out port that you can use to play back to a VCR and can also accept input for an external camera or VCR. I use this feature on mine a lot to capture video using the bullet cam.
Audio can be a bigger challenge. Unless you wondows are rolled up you'll get so much wind noise that the audio will cut out. I've been taping mics to my rear bumper and that is working pretty good.
I've got a couple of videos up on
www.streetfire.net. Just do a search for "Prelude", and you'll find my track videos on page 9 and 11.