Fantasy, I would love to see some of the more epic Dresden Files brought to life on the big screen. War between the Summer Fae and the Winter Fae with a few scraggly modern-day mortals and mages caught in the middle? Lord yes.
What I'd really like to see, although it's sci-fi, is one of Peter Hamilton's series. Night's Dawn, maybe. Galaxy-spanning space opera, like Star Wars with an understanding of how things would probably be hundreds of years into the future.