IMO, theres no way that Steven Spielberg belongs in this thread.
He is a wonderful film maker and a great director.
I can't imagine a world without Jaws, Close Encounters, Raiders, E.T, Minority report, Jurassic Park, Back to the Future, Poltergeist, Private Ryan, etc, etc. (I know that he didn't personally direct all of these movies)
I can't think of one other director who's body of work would be missed so much.