OK OK, I own a small custom car stereo shop in WA. Let me throw in my .02
First off AudioVox is ok stuff, they currently control 75% of in car theatre products, so it is no surprise that everyone is shouting there name.
Another brand to consider is Rosen, Rosen mkes all of the TV and entertainment equipment found in commercial airplanes, they have in the last 2 years started doing automobiles.
The biggest thing to look for is off-access viewing. Look at the demo screen, make sure it is playing a movie and on either side of it. Try to get as far outside as you can, so when you put it in your Van or SUV the people on the outside seats can see as well as the center seats.
THE MOST IMPORTANT THING: make sure the shop installing the unit it building a welded metal framework that is bolted to factory bolts under the headliner, then secures the DVD/Monitor unit to that. TheDVD/Monitor units can weigh as much as 20lbs. and in an accident those could kill someone if they fall out. I HAVE SEEN IT HAPPEN. Hope this helps IM me for any further details Questions about prices.