I made a decision
Just in case people were interested, I made a purchase decision yesterday. I went to BB and had the opportunity to check out the picture quality of about 10 different portable DVD players. BY FAR, the best picture quality of the ones there was the LG DP781.
It has an 8" screen and comes with a bunch of accessories (including a car mount kit). Also, I checked some reviews on CNET and other places and most seemed to like it. I'm sold.