He made the haunting Don't Look Now, with Donald Sutherland and Julie Christie as a couple in the aftermath of their child's death. The concluding horrifying reveal is one of the scariest in film history. He also made The Witches with Anjelica Huston. Seeing this at a very young age, I had nightmares with it for years after.
Clouzot gave us the incredibly thrilling and nerve racking Les Diaboliques, with one my favorite actresses Simon Signoret. Clouzot is also responsible for the incredibly difficult-to-watch The Wages of Fear and The Raven.
The master of the generic horror film, Craven has given us countless goodies, many of which have caused me some sleepless nights: The People Under the Stairs, A Nightmare on Elm Street, The Hills Have Eyes, and The Last House on the Left. And then there's the meta-comedy-horror Scream, a fantastically fun (and yet at times genuinely scary) film that, as a child of the 90s, I'll never forget.
Kubrick is responsible for one of the all-time best horror films, The Shining, as well as the best psychological and science-fiction dramas that could also be considered "horror" - that is, A Clockwork Orange. Both are among my favorite films, no matter what genre.
Hitchcock is the master of the thriller, yet horror creeps in there without a doubt. There's the obvious Psycho, which raised the standard for horror films, as well as the great Beyond a Shadow of a Doubt, Strangers on a Train, and Rear Window.
Suspiria is my preferred campy but beautiful Argento horror film, but he also gave us Inferno and Phenomena. If demons, witches, and the other creatures of black magic scare you, he's your guy.
George A. Romero
Night of the Living Dead is by far my favorite zombie film. The opening sequence at the graveyard is one of the most haunting and beautiful. Dawn of the Dead is another masterful horror film.
The king of 80s camp-horror, Carpenter gave us the great Halloween, The Thing, and The Fog - all of which have been remade, showing their lasting pleasure/horror factor. He also gave us the less "scary" yet equally fun They Live and Escape from New York.
He is not necessarily a "horror" director but has been responsible for some of the most horrific bodily images (and explosions and births) ever filmed, from such scary fare as The Fly, Scanners, Videodrome, and - a film that personally terrified me - Dead Ringers.
Bridging the thriller and horror genres, Polanski has made some of the most thrilling films that nevertheless leave you wanting to lock your doors at night - even from those you're supposed to trust. Nothing escapes the realm of the horrifying in Polanski's Rosemary's Baby, The Tenant, and Repulsion.
Another director who blurs the lines between genres, Lynch employs plenty of horror tropes to unease the viewer in his masterful films. The most unsettling of his films include Eraserhead, Blue Velvet, Lost Highway, and Mulholland Drive.