There are loads available and most are small enough to fit in front of the rear view mirror, continually overwrite, have gps for proof of speed and a built in g-sensors which, when triggered, write protects the last few recorded files in the event of a sudden stop. Basic ones can be picked up pretty cheap....
They cannot always view everywhere but the general theme is a wide angle lens which covers the front periphery of the car, the more expensive ones can have in-car view, remote playback, TFT screens etc etc but they tend to get expensive and are larger.
I'm very tempted by a roadhawk DC-1. In a car like mine the consensus is likely to be against me from the start and video proof, as well as carrying a compact in the glove box, will help to avoid said spineless scumbags taking advantage of situations, (quick photos of the 3rd party are always worth it too to help avoid those situations when a sole driver suddenly gains 1 or 2 occupants as witnesses).