7. Batman: Year One
Batman: Year One, quite possibility, could have been the greatest Batman film ever made.
That is, it could have been had it made it through the studio system without any major interference from meddling executives. Which, of course, it didn't: movie-goers got Batman Begins instead, which - as far as consolation prices go - is pretty damn good.
A proposed project from the likes of one Darren Aronofsky (he made Requiem for a Dream, so just image how dark this movie could've been), Batman: Year One would have served as a direct adaptation of the famous comic book of the same name, which focused on the start of Batman's career as a caped vigilante. A draft of the script was penned by Frank Miller, but Warner Bros. shot it down on account of the violence and some hefty changes from the comic book.
Had it been met with critical acclaim, Year One could have certainly brought in close to the billion mark; considering Aronofsky's track record, critical acclaim would have been likely.