Starcraft could make a good movie, I think. Even if you chop away all the pretty graphics and good gameplay, there's still a pretty solid storyline behind it and the expansion that can hold it's own. Something like a hybrid between the original starwars trilogy and starship troopers I would imagine, only no Fuzzy Bears (which would be a good thing).
Pretty much any Lucasfilm Games/LucasArts adventure game would work, too. Well, maybe not Grim Fandango since it would be nigh impossible to make a world of nothing but skeletons seem plausible outside of cartoonish graphics, but the Monkey Island series (almost been done already, Pirates of the Carribean rips off these games in so many ways it's not funny... except it *was* funny and very enjoyable too
) and Indiana Jones and the Fate of Atlantis would be good for action/comedy, and Full Throttle would own as a bit more serious movie. Too bad about Fandango though, since that's the best game of them all in my opinion.
