There are lots of books with the potential to make great movies, but I'm not sure if I'd want Hollywood to touch them. Examples: Any Miles Vorkosigan book by Lois McMaster Bujold and the Kris Longknife series by Mike Shepherd (aka Mike Moscoe).
I can think of one big exception to the "great book = bad movie" trend. The BBC made Terry Pratchett's "Hogfather" into a miniseries that was AWESOME. The actors were all great picks (with Terry doing a cameo as the toy store owner) and the actress who played Susan was perfect. My only minor disappointment was that Death wasn't voiced by Christopher Lee, who did the VA for the animated "Soul Music."
I think it's available for sale now; it was on BBC America around Thanksgiving last year. It was an incredibly well-done adaptation.
One of my favorite books of all time (non-sci-fi) was The World According to Garp. It was a horrible senseless waste of money and time as a movie.