I use a Roadhawk HD in car camera.
It's one of the more expensive models. It gives a really good picture. Shooting HD uses a lot of space, but standard mode gives you a lot more saving space. It has GPS andsynchronises with Google Maps so you can actually see on the map where you were driving.
The sound, if you have it turned on, is not all that good. Can be a bit distorted at times.
It doesn't have a video monitor, so you can only view the files on your computer. There is a free application which displays all the data recorded on the camera. You can also view the clips on any MP4 player, but you only get the technical data using the Roadhawk program.
This is what it looks like;
The files are saved as 1 minute long segments, but you can change the recording time if you want. It has a "G" Force monitor to detect unusual forces such as swerving, heavy braking or collisions. If an event is detected it saves separately a segment of video which includes some time before and after the event.
Here is a short sequence shot a back in April when we had the late snowfall.
I think they did a review of some of these in car cameras recently on Fifth Gear on the Discovery channel. Not sure if they do a catch up service or if you can see it again if you are on Sky.
I've had one for quite a while now. I used the Mark 1 Roadhawk before I got the HD version. The only accident I've ever captured was one that was caused by me. Nobody hurt and no police involved- Oooops.
Aword of caution if you decide to get one of these cameras. If youcause an accident and the police see you have a video camera in the car, they can use the video as evidence against you if you are prosecuted.