Studio Ghibli's latest film Arrietty is an adaptation of Mary Norton's Book, The Borrowers. I remember reading this book, and its sequel, in my Jr. High School Library. Now I want to read it again -- but I think I will see the movie first, so that I don't suffer that awful clash of "This isn't how the story is supposed to go." Miyazaki does do wonderful treatments of the books he turns into films, but time limitations do mean that he must snip subplots, combine characters, and change things.
See the trailer here.