Hmmm.. All my favourite books into movies have already been mentioned! lol
BBC version of Pride and Prejudice tops the list followed closely by the Lord of the Rings trilogy (although there were still somethings i wished were protrayed more in the movie like the Legolas\Gimli friendship, but that was minor).
A walk to remember is another one of my favs
Interview with the vampire
Marley and Me - I cried my eyes out for both the book and the movie! lol
The list of movies based on books that disappointed me is a much longer list! lol