I have a Sony digital 8 that I use with an IO Port mount on the roll bar. It's a little larger than the newest stuff, but has higher resolution than many of the smaller cameras and great stabilization. I run a remote mic ($25 from Radio Shack - it's a lapel mike with an internal watch battery) under the passenger seat to get rid of the wind noise. I also use two tie down straps to make sure the camera stays steady, which helps the picture. There is some in car from my setup at the Cobra University site, click on
http://www.cobrauniversity.com/links.htm then click on the trivia video. It was uploaded in very low res, but you can get a feel for the stabilization and sound quality.
Mike Eckhaus