This is a lovely idea for a thread!
Books and movies are two of my favorite things. It's weird, I've noticed that a lot of my favorite films were originally books, so I don't know if this say's something about me.
I agree with Sobriquet87, I think the Harry Potter movies are a pretty great adaptation of the books.
Other books to movies that I like....
Persepolis- It's a great adaptation of Marjane Satrapi's graphic novel of the same name. It's beautiful and it made me cry (both the book and the movie).
Atonement- I saw the film before I read the book so I don't know if it changed how I viewed the two but I really liked both forms of the story. It's such a visually interesting film and such a descriptive book.
Pride and Prejudice- I love both the BBC version and the 2005 adaptation.
The Help- I know this story isn't without controversy but overall I think the movie was really well done. And the book is very well written. Even if it is a touchy subject.
The Virgin Suicides- I have to admit I haven't read the book yet (but it's on my to-read list) however I think the film is lovely.
I'll probably add ton's more to this thread once I think of them...