8. The Odyssey & Iliad
The two cornerstones of western literature, the Odyssey and the Iliad have probably influenced more movies than any other work but neither of them have particularly definitive film adaptions. While Troy gave a good effort, it didn't come close to adequately doing justice to the Iliad while I don't recall any straight up adaption of the Odyssey at all. The Iliad would of course, have to create a fairly large sense of scale while also finding a way to either incorporate the gods in a believable manner (The Immortals did a serviceable job at it) or going the Troy route and eliminating it entirely. The Odyssey should be adapted into some kind of bizarre, surrealist film that becomes less and less so the closer Odysseus gets home.