This is a still was taken from my incar mount's video. I'm not sure if this still is from my Digi8 or my old Hi8.
I've used the same sort setup as SamIam for about three years. The wood with the holes for the headrest supports and a old tripod head attached in the middle. It only works if you have removeable headrests. On the focus, the rear seat has headrests...yes, I find that image stabilization works fine, but does seem to lessen the perception of speed. As does using the zoom. I would recommend a camera with a wide focal length. Long zoom is not important. You can also pick up aftermarket wide angle lenses for around $50 bucks. Its a MUST HAVE!

Anyway....bottom line is, you can't go wrong with Sony or Canon. The Digital 8 cameras (only made by Sony) probably offer the most bang for the buck but a are a bit heavier then their Mini-DV competitors. They also utilize Hi8 tapes to record on which are cheaper than mini-dv tapes. You can pick up a nice Digi8 for less then $400 bucks. JVC makes good pro-end stuff, the consumer stuff is well made but certainly lacks in picture quality compared to Sony or Canon.
Do your research. Check out www.bhphotovideo.com to compare prices and they often have some great info about their products. B&H is top notch, but beware other mailorder places (especially Broadway Video.) Check out videomaker magazine for reviews, they carry it at Barnes & Nobles.
Good luck.
-Ben