9) Edward Furlong
Most known for playing the future saviour of mankind John Connor in Terminator 2: Judgement Day, Edward Furlong could have been a hero in the short term too if he had been cast as Spider-Man.
As Spider-fans may know, James Cameron tried to get a Spider-Man movie off the ground throughout the 1990s. In 1995, the film was ready to go with Furlong as Peter, Drew Barrymore as Gwen Stacy and possibly Katherine Hepburn as Aunt May. The villains would have been Lance Henriksen as the Green Goblin (who would have killed Gwen) and Arnold Schwarzenegger as Doctor Octopus (who probably would have made a load of octopus puns).
Unfortunately, the production company Carolco went bankrupt and so Cameron moved on to do some little film called Titanic. Bad move there, pal.