go to
www.actioncameras.co.uk
we use them for work...awesome company to deal with.
and imho the best kit at reasonable prices
ideally if its quality you are after, I would discount HD cameras as the quality still isn't there.
I would go for a camera ( bullet) type, hard wired to a camcorder in the car and controlled via a lanc remote.
If you then require live audio feed back get a decent mic.
You might find placing a mic under the bonnet tricky as you need to baffle out the wind.
You might need to wrap something around the cabling to protect it from the heat.
You need to make sure your camera is compatible with a bullet cam.
it needs to have AV in/out.
The BBC even use Actioncameras for some of there stuff.