6. Martian Manhunter - Nicolas Cage
Say what you will about Cage's recent outings with his latest entries on his filmography; Cage was a 90s powerhouse and was really able to strut his stuff. With Face/Off, Con Air, The Rock, and an Academy Award for Best Actor in Leaving Las Vegas, it's hard to see how Cage wouldn't be involved in the biggest action film of the year. He had the fans, the gusto, and was even up for Superman for Tim Burton. His Manhunter would have been all kinds of sedated, quirky strangeness, and it's likely that it would be a role Cage could completely get lost in. While he might be a bit busy with Johnny Blaze and quick-fix films like Stolen and The Frozen Ground right now, it doesn't hurt to dream about the what-could-have-beens. And I think it's safe to say that Cage could have made quite the interesting Martian Manhunter in his prime.
Alternate: Denzel Washington