Jurassic Park (book is still better though)

To Kill A Mockingbird

Actually a tough question but I will go with The Lord of the Rings trilogy. Perhaps because I did not read the books until The Hobbit movies were being made, but I thought Jackson did fantastic work in bringing those stories to the big screen, unlike his work on The Hobbit.

Jaws is also a great choice. Jurassic Park the book is so much better than the movie, which in itself was great but I was frustrated with all the great stuff from the book that did not make it to the screen.

My first thought was Tom Clancy. I thought The Hunt For Red October was a good movie but it was an abortion of the awesome novel that Clancy wrote. Patriot Games was awful. Clear and Present Danger was a good movie but was not in the same league as the book - I never bought Harrison Ford as Jack Ryan and hated Willemstad Dafoe as Clark. The Sum of All Fears, possibly Clancy's best book about Muslim terrorists detonating a nuke at the Super Bowl, but in the name of politically correct cowardice, Hollywood gives us a movie about white Germans instigating war between the US and the USSR.

The Godfather
One Flew Over the Cuckoo's Nest
To Kill a Mockingbird

The Godfather is the answer to a question about adaptations that were better than the book.

Busty Schoolgirls Need Deep Lessons was pretty well adapted. The screenplay suffered due to some artistic dialog but otherwise it was fantastically done.

No country for old men was a fantastic adaption of Cormac McCarthy's novel.

Lonesome Dove