It's a question as old as the movies - which is better, the book or the film?

With some genres, most notably Science Fiction and Fantasy. there is no comparison - the book outshines the movie adaption in almost every respect. With other genres the distinction is not so clear. This is perhaps most with the horror genre.

Three of my all-time favorite horror books are The Exorcist, The Omen and Clive Barker's Books of Blood. The movie adaptions of The Exorcist and The Omen were both excellent in my view, adding a certain atmosphere that enhanced, rather than detracted from, the original book story. Books of Blood was a terrible movie adaption.

What do you think? Are there any instances where you think the movie is better than the book?