I really think that Andrei Tarkovsky is the greatest!  But besides him there are:
Fellini
Bunuel
Bergman
Scorsese
Neil Jordan
Mike Leigh
Lars Von Trier
Vittorio De Sica
Kurosowa
Truofaut
Godard
Kubrick
Errol Morris(Even though he does documentaries)
Woody Allen
Dreyer
Darren Aronofsky
I know that there are hundreds that I have foregotten