One of my writer's lists is discussing movies adaptations from books. One of the topics is "Has anyone seen a movie version that was better than the book?"
I'm not sure this is ever going to be a fair comparison. While any screenwriter who changes the ending or basic plot elements of a story for the adaptation should be condemned to writing late night infomercials for the rest of his/her/hir life, film is a different medium and what works in books won't always work on screen. Books can have scope and scale in setting that no movie special effects wizard can ever match, because books tap into a reader's imagination, which has no budget and isn't limited by those pesky laws of physics. Not to mention that every reader internalizes and interprets a writer's words through a unique filter, so even if a movie were able to capture one reader's vision of the story, every other reader would still be saying, "Hey, that's all wrong." Movies, however, convey action in a way that books can never match.
Books aren't limited by time, so they can go into detail that simply can't make the translation onto the screen. A great example of this is the Harry Potter movies. Much of the conflict with his Aunt, Uncle, and cousin had to be cut. So did a lot of other stuff, sometimes to the point where I wonder if someone who hasn't read the books can follow the movie. Ten or twenty years from now, someone will make new Harry Potter movies. Maybe they'll do it in a mini-series format that explores the interpersonal relationships in more detail, but even that version would have to sacrifice something from the books (probably the special effects).
I've seen one movie adaptation that I felt transcended the source book - The Grifters. Maybe because I saw the movie first and it remains one of my all time favorite movies. On the other hand, I saw a couple film versions of Rebeca before I read the book, and I don't think any film version does the novel justice. And to even it out - I love the movie Blade Runner, and I'm a huge fan of Do Androids Dream of Electric Sheep (theoretically the source book), as long as I don't try to compare the two. Not that they can be compared. They're not the same story. But each is an example of outstanding work in their respective mediums.