I think it's always interesting to see how a book transitions into a movie. Most times, I think the books are better, sometimes I feel that each are good in their own right, but rarely do I feel a movie is better than a book. Here's my take on a few of my favorites...
I think most Stephen King books are much better than the movies. There's something about Stephen King's books that don't translate well into film.
The Lord of The Rings trilogy - Peter Jackson made the books come alive and created artistic genious in the movies.
The Lovely Bones - movie & book equally moving, I was on the edge of my seat watching the movie and I already knew what was going to happen!
The Twilight Saga - Books are better, but movies can stand on their own.
The Harry Potter series - The first two movies were a little tame, but then Bam! they picked up after that.
Eragon - movie sucked, book rocks