4. Copperhead
If you've never heard of Copperhead, don't worry. You aren't alone. Copperhead was an incredibly interesting project involving zombie flick mastermind George A. Romero, that would have been a cross-media event for Marvel. In the late 80's Jim Shooter, the controversial editor-in-chief of Marvel at the time, approached Romero after seeing Dawn of the Dead. Shooter wanted to create a character that would simultaneously be introduced in comic and in film, called Copperhead. Copperhead was a cyborg and Philadelphia sheriff in the not-too-distant future. Marvel writer Bob Layton called the project "Romero's Star Wars," and said it was to be "a very ambitious project with huge, sweeping visuals and massive SPX." The project was put on hold so that Romero could finish his next project, Day of the Dead, which he was going to use as proof that he could handle a film with a bigger budget and complicated special effects. Unfortunately, he was forced to take a smaller approach to Day of the Dead after backers refused his original plans, and the film underperformed both critically and financially. The Copperhead producers then got cold feet, and the project dissolved into nothing. Geeks of Doom wrote a great writeup of the entire story that you can read
here. Copperhead would have predated both Robocop and Terminator, and if it had actually gotten made, could have been a great 80's action movie and highly original entry into the superhero film genre.