Check out CircuitCity. I stopped by there a few weeks ago and they had 3-4 DVD systems just for cars even a VHS (????) one.
There prices are relatively expensive to the prices you can find online but at least you can take a look at the quality of the lcds/full car units.
I spotted a couple of LCDs at BestBuy ie ceiling mounted lcds for the roof of the car pretty nice I didn't see any dvd car units though.