1. Mrs. Doubtfire based on Alias Madame Doubtfire by Anne Fine
Who knew Mrs. Doubtfire was a book, and by Anne Fine no less? When I saw this at the library I work at, I was floored.
2. Shrek, based on Shrek! by William Steig
The book is pretty different from the movie, I have to say, but I still love William Steig. I'm pretty sure the only similarity is that it's about an ogre named Shrek who goes to look for a wife. Though the ending isn't as happily-ever-after as DreamWorks decided it should be. Still, I like both.
3. The Great Mouse Detective, based on Basil of Baker Street by Eve Titus
Who remembers this movie? Ah, the good old days. I kind of feel like I have to read this book now. Look at the delightful cover!
4. Jumanji, based on Jumanji by Chris van Allsburg
This one is probably much better known as a Newbery-award winning book, but some people still might not know. Again, the book is pretty different (alas, no Robin Williams character, who I just realized is making a few appearances on this post's list), but both are very enjoyable.
5. Fly Away Home, based on Father Goose: One Man, a Gaggle of Geese, and Their Real Life Incredible Journey South by Bill Lishman
I guess they figured no kid would want to see a movie about a guy who wanted to see what would happen if he tried to lead some Canada geese south, so they threw in Anna Paquin and made the geese orphans. Check out Lishman's Wikipedia article here, which kind of explains what he was trying to do.
6. Homeward Bound, based on The Incredible Journey by Sheila Burnford
Okay, okay, I know most everyone knows this is a book, but I figured I'd throw it on there for the hell of it. This movie has a pretty great soundtrack, by the way. Oh hey, one cool thing I just noticed in writing this post is the family that owns the pets are called the Burnfords, which is the name of the author. Also, look—it was a Disney movie in 1963 too.
There you have it, folks. Any that I missed? I love having my mind blown by stuff like this, so don't hold back.