I found a bunch of double-din touchscreen head units at www.sonicelectronix.com. There are quite a few around the $300 mark and seem to offer a lot of options:
5.1 audio pre-outs
USB inputs
A/V inputs
iPod ready or compatible
SD memory card reader
video outputs
TV-tuner
etc


Some of the SNR aren't too stellar and I'm sure the built-in amps aren't all that great but is there any other reason not to try them out? They are less than half the cost of similarly spec'd brand name HU's so they are looking pretty attractive.

 

I'm thinking they would be the same quality as the portable DVD players.

You'll notice the generic brands has really terrible picture quality and the color bleeds. Even using the video out and connecting it to a different TV in my house displayed poor pictures.