There are plenty of films which far outstrip the novel on which it was based.
Forrest Gump: Winston Groom's novel is as charming and endearing as it's protagonist, but it lacks the realism and humour of the film. I know it may seem questionable to suggest the film is realistic, but in comparison to the novel Forrest's escapades are mundane. The novel is also written entirely in phonetics, and whilst this is a humorous novelty for the first few chapters it soon loses it's charm.
Fight Club: This has already been mentioned, but the film is in an entirely different league to Chuck Palahniuk's novel. The novel is repetetive and quite a strain to read in terms of staying interested. The film is sharp, witty and far more ground-breaking in terms of its treatment of the content. I'm not suggesting the book isn't good however, it just doesn't compare to the film. Fincher is a genius.

There are many more such as Trainspotting, Psycho (who can deny the supremacy of Hitchcock's masterpiece!?), The Reader, and many more.

I agree with Lauren on Stardust - I wouldn't necessarily say the movie was better, but it was a very different mood. The book had a sort of Grimm's fairy-tale feel, while the movie was humorous high adventure, and had a lot more punch to it.

FzingWizbee makes me sad, though. I know a lot of people feel that way about Howl's Moving Castle, but it's my favorite book and I really didn't like the changes made in the movie!

I have to agree with David on "Wonder Boys," it's the first one that came to mind. A perennial favorite.

Double Indemnity

I would agree that Gone with the Wind is better as a film; however, I think the book is brilliant as well. Vivien Leigh just took the character Scarlet and ran away with it. It is my favorite female performance. I would also say that the mini-series of The Thorn Birds is better than the book. I would disagree about Interview with the Vampire...the book is one of two that made me weep.

Personally, I felt that the film version of Howl's Moving Castle had more charismatic characters. Not only that, but the film was a much stronger depiction of the plot.

Porkey's Revenge... OH? It wasn't previously published. Hmmm, I thought it was a MAD magazine short story! I'm crestfallen!

Haste yee back ;-)

Little Children. I hate reading "kidspeak" in books, and that killed most of the book for me. Plus, Todd Field is a master of mood.

I just can remember Fight Club -a great novel with a very bad end- and A Clockwork Orange

The Horse Whisperer. The book was great right up until the ending, which left me muddled and confused. Redford fixed the ending in the movie.

I'm tempted to say The godfather, but I haven't actually read it. Could the novel be better, though? I doubt it.

Inkheart. The movie did a much better job of developing the characters and making them interesting, especially Meggie, while the book meandered its way to an unsatisfying ending.

"Stardust." The book was fantasy oriented with a depressing ending and lackluster plot. The movie was fantasy oriented with an adorable ending and an engaging (and sometimes hilarious) plot.

High Fidelity. So much more fun than the book, and the casting was spot on.

"The Devil Wears Prada" "Adapatation." "The Wizard of Oz." "Gone With the Wind" (although the book was terrific!)

Jurassic Park - at least you got to see the dinosaurs, which was the whole point. Reading about a T Rex pales in comparison to actually seeing one.

Fight Club - the book was dark and disturbing, while the move was dark, disturbing and funny. They are almost two different animals, and the dual identity works better in the movie than it does in the book.

Cronenberg has a quote (can't find it online, but I believe it was about adapting Naked Lunch) about how a film maker has to be disloyal to the author's intention when making a film in order to truly adapt a novel.

Interview with the Vampire. The movie's ending crushes the novel's ending.

Twilight. The books are addictive, but the movie was in on the absurdity.

I think "Wonder Boys" is better as a film, which is ironic since it's about novelists. But the story is streamlined and tightened for the film where the novel has a few random digressions and a sequence midway through that stops the book cold. There aren't enough digressions in the book to make it seem like a stylistic choice, and after the book stops dead, it takes a while to get back into gear.

The film wisely cuts out that sequence without losing any of the seemingly aimless wandering of the characters. I read the book and enjoyed it well enough. I've watched the movie several times, it's one of the five I'd take with me to a desert island. (Along with a DVD player and a generator, obviously.) Every time I've seen it, when it's over, I have the urge to go and write no matter what time of day or night it might be.

If you wanted to include nonfiction books, then I'd also suggest "All the President's Men."

I don't think a movie can be greater than a great book, but it can be a fine complement. Dune by Frank Herbert had real depth as a book, meaning more with each reading. The movie filled in and augmented, but could never replace. There are movies I can view pleasurably several times, but none that get markedly deeper with repetition.

I enjoyed the "Lord of the Rings" movies MUCH more than the books. I respect Tolkien's creative achievement, but the books felt like they went on...and on...and on, and not in a good way. And that weird, anti-climactic section in the Shire at the end of "The Return of the King?" Great idea to leave it out of the movie. I liked "The Hobbit" book much more than the LOTR series, so it will be interesting to see how that film shapes up.

Silence of the Lambs ... great acting makes the characters come alive even more than your imagination could ...

As terrible as The Da Vinci Code the film was, it was still better than the book.