Before the original Ghostbusters came around, Ivan Reitman, Bill Murray and Dan Aykroyd were in talks to make Hitchhiker's Guide to the Galaxy. It was scrapped when Aykroyd came up with the idea for Ghostbusters.
It's recently come out that they won't be making a Lone Ranger movie staring Johnny Depp, but we all know that's not the only potentially awesome movie that Hollywood canned prematurely. Cracked has a great list of 10 others that were cancelled for a variety of movies. Of course, I'm sure I'm not the only one here who desperately wishes the Ghostbusters 3 movie actually went forward at some point. They also have a few unrelated but fun trivia facts like this one:
Of course, a lot of the other ones would be pretty awesome too.Link