I don't go with the crowd on this one. I hate Kubrick's THE SHINING but think that CARRIE is definitely one of the best. If you like films that SUGGEST rather than show everything, Robert Wise's THE HAUNTING is certainly a superior tale of terror. For horror as in exploration of the darker side of human nature, WITCHFINDER GENERAL (known as THE CONQUEROR WORM in the US) and the original version of THE WICKER MAN are two brilliant films.
Nosferatu Le Yaux sans Visage Night of the Demon Mad Love Frankenstein (1931) Isle of the Dead They came from Within Miracle Mile Testament the Beyond The Exorcist Suspiria Rosemarys Baby Deathdream Quatermass and the Pit It Lives Dead End The Gift The Sixth Sense
Friedkin's The Exorcist, Kubrick's The Shining, Zulawski's Possession, Suspiria, New York Ripper, Cannibal Holocaust, Psycho 2... and honorable mention goes to American Psycho (not really a horror film, I know!), and of course Zombie Flesh Eaters.