Oz the Great and Powerful (2013)

It's just been confirmed that Sam Raimi (Legend of the Seeker, Spartacus) will direct Oz the Great and Powerful, a prequel of sorts to The Wizard of Oz, with Robert Downey, Jr., expected to play the wizard.

Update as of January 20, 2011: Robert Downey Jr. is no longer attached to the film. Johnny Depp is being named as a contender for the role.
Update as of February 4: Johnny Depp considered role but no. James Franco is now the name being dropped.

Plot details from Pajiba

"We also knew that the movie would focus on a younger wizard, and his origins in the Land of Oz. Thanks to the Hollywood Cog, we now know quite a few details about Mitchell Kapner’s story, which would have the Wizard — a snake-oil salesman posing as a magician — enter Oz via a hot-air balloon, which he uses to escape an angry husband who has found out that Oz slept with his wife. There, Oz — a fast-talking huckster who wears a velveteen frock coat (yes, I can see that) — falls in love with Glinda (the Good Witch), and the two combine forces to Fight the Evil Witches Evanora and Theodora. Theodora starts out as a good witch, but after Oz jilts her sexual advances, Evanora — the truly evil witch — convinces Theodora to become an evil witch with her and help her to rule all of Oz."