Who Framed Roger Rabbit? based on Who Censored Roger Rabbit by Gary K. Wolf
I feel like this one always shows up on lists like these, but I just couldn't resist. I haven't read this one, but I remember the movie well from childhood. Mostly how it freaked me out. It's a good thing it wasn't based too closely on the book, because I would never have been able to sleep again.
The Descendants by Kaui Hart Hemmings
As someone who has seen the movie and read the book, I have to say I liked the movie better. However, it wouldn't even exist without the book, especially since most of the dialogue was pretty much just lifted right out of the novel.
The Town based on The Prince of Thieves by Chuck Hogan
This one more people might know about. I knew about this one because I worked at a bookstore when the movie came out. I haven't read or seen this one, so I won't be much help there. But I can tell you it was set in Charlestown, in Boston!
Field of Dreams based on Shoeless Joe by W.P. Kinsella
I feel like I knew about this one before, but forgot. Anyway, I knew about the book and of course I knew about the movie, and now I know they're connected!
Fast Times at Ridgemont High based on book of the same name by Cameron Crowe
Who knew? I kind of want to read the book.
Die Hard based on Nothing Lasts Forever by Roderick Thorp
Die Hard is pretty awesome. I haven't read this book either, unfortunately, so I can't attest to how closely the movie follows, but hey! Another "who knew" moment.
Those are only a few movies based on less-well-known books out there. I know I'm missing a lot of them including the one I thought of that inspired me to write this post (curses!), so please leave them in the comments!