There is also a magnetic clamp available which fits to any standard camcorder - you stick this to the tank or filler cap and it films through the windshield - very handy if you happen to be speeding and the police want corroborating evidence
The most elaborate I've seen which I'm not sure is even commerically avaialble is a replacement filler cap with a camera shoe attached to it.
Sorry, I'll try to update this post if I find url's for the above products.