I've got this one ( Pioneer Universal Rearview Camera NDBC1 ) mounted just above my license plate on my Mercedes Benz GL450. You can hardly see it. Best part is that it comes on automatically when you put the car in reverse. It's wired to the reverse lights which is all the light you need. Looks fantastic at night. It appears to be smaller than these other units posted.
http://www.abtelectronics.com/product/19180.html