If they have it, the remake of Dune, Dune Messiah and Children of Dune should take up about 8 hours. They aren't anywhere near as good as the books, but are passable. Lawrence of Arabia and Ghandi would do the trick too, if you're looking for something meatier.

Personally, I'd just bring one of [url=http://www.thinkgeek.com/computing/mp3/98d3/]these[/url] and watch whatever the fuck I wanted to. Extra geek points for wearing VR goggles on a flight and cracking up as loudly as possible to Borat/Office Space/Flesh Gordon. Preferably while others are watching something serious or trying to sleep.

And yes, I do have one. Personally, I wish that the resolution was a bit better. But otherwise it works wonderfully.