A movie just as good as the book
 

Charlie and the Chocolate Factory, the 60's version.

The Wizard of Oz

The Ten Commandments - Seriously.

All deviate greatly from the source material. For good reason. Books are not movies, they need to be rewritten as movies.

I'm blanking on more, anyone have any? Most of the time there's no comparison.

The Shining (Kubrick's version, naturally.)

Gone with the Wind

Jurassic Park.

A personal favorite - Somewhere in Time by Richard Matheson (Published as "Bid Time Return"- also wrote I am Legend)

Maltese Falcon by Dashiell Hammett

The Godfather
Dances with Wolves
Fried Green Tomatoes
The Green Mile
Shawshank
HP: Prisoner of Azkaban
LOTR:FOTR
Maurice
Object of My Affection
&
that gay cowboy movie...

:)

One Flew Over the Cuckoo's Nest

To Kill a Mockingbird

Blade Runner (book titled Do Androids Dream of Electric Sheep, and I think in this case I actually prefer the film, though the book is quite good)

Ferdinand the Bull (the Disney animation is every bit as delightful, maybe even more so, than the book on which its based)

The Many Adventures of Winnie the Pooh comes to mind
and I am with Borneo on The Maltese Falcon
The Godfather

I need to think, think, think on this more

Tons and tons of movies are better than the books. They tend to be movies based on books that either weren't all that good or obscure.

As examples of this I'd mention Planet of the Apes, Bridge Over the River Kwai, Psycho, The Exorcist, Midnight Cowboy, Ordinary People.
As for good movies and good books I'd say that The Prestige was as good as the good and maybe better because it was willing to make changes for the medium. The Pillow Book is a great example of someting working in print and then being transformed to a visual medium.

The Cat in the Hat (animated version)
Carrie
The Hunt for Red October
The Godfather
From Here to Eternity
I, Claudius (actually a miniseries, but awesome)