I have been looking for the same thing (2 kids on long haul flights) and so far I am close to purchasing the following: Shinco SDP-1720 7" TFT LCD Portable DVD player from allcam:
http://www.allcam.biz/products/shinco_dvd.html for £199. It appears to be well rated and OEM manufacturer for the 'big boys'. Also check out the accessories at allcam. They sell holders for the back of your car seat so rear passengers can watch, and extra batteries (about £45). Battery life for this model is approx 3 hrs (forum users report 3.5 hours). They also sell a universal battery which purportedly lasts for 5 hours, this would give you 8 hours runtime without recharging. Screen is 7”, multiregion compatible with more DVD formats than I can be bothered to type as well as CD formats, MP3 etc. Full spec is on allcam. Player has very good reviews and the only problem seems to be whether you choose 7, 8 or 9 inch. Seems also to be well rated as a standalone, can also plug in your video camera and digital camera for viewing images/films. Firebox also have these players:
http://www.firebox.co.uk/index.html?...roduct&pid=825, but allcam has better accessories and has them in stock. Also make sure you buy SDP-1720 and not the SDP-1731A (cheaper model same spec made for Walmart, not as good quality(
Anyway hope this is helpful.
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