Everyone has seen the famous movie The Wizard of Oz, but few know it was based on a book. More specifically it was based on a series of books written by L. Frank Baum. I used to love reading the Oz books when I was a little kid so I tracked down a list of the Oz books. There 14 written by Baum, and many more written by others.

By L. Frank Baum
The Wizard of Oz
The Land of Oz
Ozma of Oz
Dorothy and the Wizard in Oz
The Road to Oz
The Emerald City of Oz
The Patchwork Girl of Oz
Tik-Tok of Oz
The Scarecrow of Oz
The Lost Princess of Oz
The Tin Woodman of Oz
The Magic of Oz
Glinda of Oz

Other Oz Books
The Royal Book of Oz (Thompson--although R&L editions say Baum, 1921)
Kabumpo in Oz (Thompson, 1922)
The Cowardly Lion of Oz (Thompson, 1923)
Grampa in Oz (Thompson, 1924)
The Lost King of Oz (Thompson, 1925)
The Hungry Tiger of Oz (Thompson, 1926)
The Gnome King of Oz (Thompson, 1927)
The Giant Horse of Oz (Thompson, 1928)
Jack Pumpkinhead of Oz (Thompson, 1929)
The Yellow Knight of Oz (Thompson, 1930)
Pirates in Oz (Thompson, 1931)
The Purple Prince of Oz (Thompson, 1932)
Ojo in Oz (Thompson, 1933)
Speedy in Oz (Thompson, 1934)
The Wishing Horse of Oz (Thompson, 1935)
Captain Salt in Oz (Thompson, 1936)
Handy Mandy in Oz (Thompson, 1937)
The Silver Princess in Oz (Thompson, 1938)
Ozoplaning With the Wizard of Oz (Thompson, 1939)
The Wonder City of Oz (Neill, 1940)
The Scalawagons of Oz (Neill, 1941)
Lucky Bucky in Oz (Neill, 1942)
The Magical Mimics in Oz (Snow, 1946)
The Shaggy Man of Oz (Snow, 1949)
The Hidden Valley of Oz (Cosgrove, 1951)
Merry Go Round in Oz (McGraw and Wagner, 1963)

Information borrowed from: Oz FAQ, Oz Books, WikiPedia, and of course Google.