After thorough research, in December we chose the Panasonic LS90 (a 9" screen) for our son, as extra entertainment during our frequent long-hauls. Absolutely stoked with it!

As PP said, battery life is key - we're getting *at least* 8 hours out of it set to low brightness (which doesn't at all look low to me, doesn't compromise quality at all). I couldn't find anything else in the market that came close to this battery life. Overall product quality is excellent, too (two headphone jacks, plays a host of input media, connect to TV in hotel rooms without DVD players etc etc)

HTH