Well, there's been various Lord of the Rings games. The one I'd like to single out is War in Middle Earth, which came out in 1988, well before Peter Jackson's movies and after the 1978 one. It can vary heavily from the books, with the game not ending unless the bad guys take over the world and/or get the ring back. Frodo & co. can suffer a TPK, Minas Tirith can fall, and you can still win.
There's also Betrayal at Krondor and Return to Krondor, both based on Raymond Feist's Midkemia series. Again, you can wander nearly anywhere and there's lots of sidequests to pick up in addition to the main plot. This is a series that would make a solid movie or three, but is maybe too similar in setting to LotR for it to happen.
Oh, and there's been a few Dune games, too, both pre- and post-movie.
A game based on Ender's game would be pretty cool. That would certainly transition well.
I'm not sure what genre, but a game set in either Asmimov's Robots or Foundation (are they one now?) universes would be interesting.
It would also be nice to see something based on Terry Brooks's works.