I helped work with some fourth grade readers this year. One of the novels they read (and I read with them) was The Wizard of Oz by Frank Baum.
As is typically the case, the book is pretty different than the movie. This group of students seemed to like it, and they enjoyed picking out the differences between book and screen. (Though this exercise did create some confusion when it came their "test" time). I did not realize that this was the first book in a long series by L. Frank Baum. Personally, I am not interested int he sequels. The book, however, prompted me to put the Gregory Maguire book Wicked back on my "To Read" list.