In recent years the majority of digital cameras have added video capture as a feature. Some of these shoot 640x480x30fps onto solid state memory chips. This, in effect, gives you a 2-for-1 feature that I find very useful - shoot stills and video on one camera and edit them later. The solid state memory makes recording on rough surfaces possible and memory chips are cheap [I get 1hr of video on a 4GB SD chip along with several hundred pictures.]. If you want HD then you're probably going to have to buy a specific HD video camera.
I use a Canon G7 but have had problems with image bounce. Evidently image stabilization only works in picture mode.
Still, on smooth roads it does a good job. I've got a RAM mount on the hydraulic reservoir and shoot through the windshield so it appears that the vibration is coming through the front end. I've been investigating a helmet mounted camera and remote recorder [$6-800] but the G7 is paid for and I can shoot OK with cruise control on or one-handed.
I'd suggest using what you have if your digital camera supports video. Either way, I'd suggest a careful evaluation of mounting systems as vibration can make good video difficult to view [Apple is coming out with a vibration reduction feature in their 09 version of iLife/iMovie that seems to remove most of the vibration - at least in the promos].
And please post what you discover works best. We're all looking for ways to take better video.
