Starship Troopers.
Congo and Sphere come to mind.
Other movies off the top of my head:
[...]
Eragon
movies that ruin books are easy to list... movies that didn't ruin books are less likely
You're implying that was a good book to begin with.
Hannibal, the book was kick ass, but the movie neutered its so bad, it was not funny. I can't believe they took out he electric eel.