1. Brokeback Mountain. The movie was fabulous, and captured the relationship between the two men far better than the book. The book didn't have me thinking "I can't quit you!" (A random aside - is it just me that looks twice at the guys in the Speights ads now?)
2. Once Were Warriors. Alan Duff cannot write. The movie was good, but I would rather poke nails through my eyelids than read anything else written by that man.
3. Zodiac. I loved the movie, but found that in the book the author was too busy telling the story of himself being fantastic to hold my interest.
4. The English Patient. The movie was beautiful. The book was good, but also quite pretentious, at times so over-written I wanted to vomit in my own mouth, and much clumsier in its execution than the movie. Apparently, the book is 'post-colonialism', which explains why it is the way it is. I don't care. Putting an 'ism' on the end of a phrase doesn't necessarily make the book in question a great book. Sometimes I wonder if people are scared to criticise pretentious writing as they fear looking stupid, like they didn't "get" it, when all we need is the little child to yell "but the Emperor is wearing no clothes!"
5. Children of Men. They were both flawed, but the way P.D. James painted the world inhabited by the characters was not as strong as that shown in the movie. I also preferred the adapted plot in the movie.
6. The Constant Gardener. The book was good, but the movie had a heart and soul to it that the book lacked. I empathised with the characters in the movie far more than in the book, and got much more emotionally involved.
7. The Three Musketeers. At least I could finish the movie. The book still sits on our bedside table with a book mark permanently living about half way through.
8. Forest Gump. The book really disappointed me on account of being wayyyy too random.
9. The Joy Luck Club. While the book is lovely, the movie is more coherent and, as a result, better.
10. Clueless / Emma. This was a left field adaption, but I just got more pleasure from Clueless than I did from Emma. Maybe it was because Emma didn't carry a phone that looked like a brick. Heh.
Some other people have come up with a few more that I can't comment on as haven't read the books, but thought I'd post anyway. Namely Sense and Sensibility, Whale Rider, The Pianist, and Bladerunner/Do Androids Dream of Electric Sheep. Disagree? Got more to add?