Directors who make great films:
David Cronenberg: Videodrome, Naked Lunch, A History of Violence
Probably my favorite director. He can do the weird/disturbing/surreal/gross better than just about everyone save maybe David Lynch in Eraserhead, and is also phenomenal at the ultra-realistic and gritty. Goddamn, he's amazing/
Quentin Tarantino: Reservoir Dogs, Inglourious Basterds, Pulp Fiction
Writes the best dialogue I have ever heard in a movie. Reservoir Dogs is also my favorite movie, it's an absolute masterpeice. Kill Bill, Death Proof and From Dusk Till Dawn (that one in a good way) were kind of awful, but Reservoir Dogs, Inglourious Basterds, Pulp Fiction redeem any bad he could have done.
Stanley Kubrick: A Clockwork Orange, Dr. Strangelove, Full Metal Jacket
Awesomeand arguably the best director of all time. He really can(could) do no wrong, although I have heard Eyes Wide Shut was terrible, I have not seen it so I'm sticking to my claim. A Clockwork Orange alone is a perfect film, not to mention his many other classics.
Directors who make great movies:
John Carpenter: They Live, The Thing, Escape from New York
Fantastic at corny action, decent at legitimate horror (beyond Halloween...eh.) They Live and Escape from New York are essential for awesomely bad action, and The Thing has some of the coolest real effects of any movie of it's time.
Kevin Smith: Clerks (+II), Dogma, Chasing Amy
Hesitant about this one because of the atrocities he has been responsible for (Mallrats,Jersey Girl,the most recent cop one with Bruce Willis), but Clerks is one of my favorite movies of all time, the other are great too. Second to Tarantino for my favorite dialogue.
George Romero: Day of the Dead, Dawn of the Dead, The Crazies
The only thing preventing this from going in the 'films' section is the terrible acting in most(if not all) of his movies. Day of the Dead is the most underrated of his works, I would say it's the best(and darkest) of the Dead series. The Crazies, Martin and Creepshow are fantastic too.