Harry Potter: This seems like an obvious starting place. Come on, picture character creation: What house did the sorting hat place you in? Do you favor charms, curses, maybe broomsticks? prophecy? I'm not the biggest Potter geek, but I have to give the series credit: the world is lavish, and I want to run around Hogwarts, and Diagon Ally.
Night Watch: This is a Russian book/movie series. Personally, I enjoyed the first novel, but preferred the movie series. It sounds like a basic mythology (but is very well executed): There are Others who are light or dark. Over time, they realized they'd destroy each other if they continued to fight. They have a treaty, of sorts. The light watches over night, and the dark watches over day. They make sure neither side gets to powerful. The world and magic of the world is flavorful enough that it could be its own game franchise. Really though, there's no reason why you couldn't just adapt the World of Darkness (Mage specifically) to play a Night Watch game.
The Kingkiller Chronicle (The Name of the Wind): So far Rothfuss has only released the first book, but The Name of the Wind has wowed both the press and legends in the fantasy field (Ursula K. Le Guin, Orson Scott Card). The series has hardly begun to explore the rich mythology of the world but we already have humans, fey, as well as darker, stranger creatures (I love the Chandrian) . We have an academy (great base location for any game), cool magic: sympathy and whatever knowing the name of something is called (it's been awhile since I read the book). I'm anxious to see where the series goes, but also anxious to see if a game gets made based on this series.
Kingdom Hearts: I like this series too much. Really though, the game offers up many fun, classic Disney worlds, as well as original worlds. You have standard Final Fantasy classes, as well as the Keyblade wielder.
Who Framed Roger Rabbit? I'm not kidding. Film noir world + Cartoon world = two unique worlds that offer players the ability to be vastly different kinds of characters. The one problem: What the hell would you do in this game?
The Matrix: Another obvious choice. Next.
Sandman: Obvious as well. Damn.
Okay, I'll just say there's any number of other fantasy books or vertigo comic book series that I'd like to see made into games. I really don't need to catalog everyone of them. Anything you'd like to see made into a game?