The redant isn't the biggest, but it is the least expensive. Clarion makes a 10" widescreen, panasonic makes some really big widescreen lcds. In your dash, you should have room below the gauges to tuck the rest of a 4:3 screen, if you don't mind doing surgery. a 10" 4:3 screen will only be 6" -7" tall, it wouldn't take much hiding.
OH YEAH, then you could watch DVDs in your gauges

real safe on the long road trips... Have the speedometer overlay on the movie...