I'm surprised nobody has mentioned Quentin Tarantino! (Reservoir Dogs, Pulp Fiction, Kill Bill, Death Proof, Inglourious Basterds)
Or the Wachowski brothers (The Matrix series, V for Vendetta)
Or Ridley Scott (Alien, Blade Runner, Legend, Gladiator, Black Hawk Down, Kingdom of Heaven, etc.)
Have to agree with all the obvious ones people have mentioned already, especially George Lucas, Steven Spielberg, Michael Straczynski, and a host of others.