Orson Welles' Batman
Yep, you read that headline correctly. Back in 1944 Orson Welles, genius director and auteur, was preparing a version of the Batman story for the big screen. He had gone as far as having a screen treatment written up, had started production design, and had even gotten some stars lined up! You can read the whole story at Mark Millar's column at Comic Book Resources.
Apparently, the movie would have begun with the origin story, the death of his parents by street criminals leaving him orphaned. It would have ended with a battle to the death with the Joker, the Riddler, Two-Face and the Catwoman facing a demasked Batman. Imagine what Welles could have done with that! It would have brought the comics and superheroes into a realm of adult content and consideration. It would have changed the landscape of films forever.
The cast? Try Basil Rathbone as the Joker; James Cagney as the Riddler; George Raft as Two-Face; Marlene Deitrich (!!) as Catwoman. What scuttled the project was that Welles wanted to take the role of Bruce Wayne/Batman; the studio wanted someone like Gregory Peck (!!). Remember, this was when Welles was still a tall, relatively svelte man. Imagine that sonorous voice, like a rumble from the Depths of Darkness, issuing warnings to the bad guys.
It would have been awesome. Read the whole column, which has more stuff.