You have to love a movie called Evil Dead because it lays right out for you, what's going on. It's about the "dead" who are coming back to life. And they're "evil." These aren't friendly spirits like in Ghost. Hence, Evil Dead. It's basically a very low budget gore film about a group of friends who go out to a remote cabin the woods, and the phrase "remote cabin in the woods," can never be a good thing. They get attacked by these spirits and all mayhem breaks lose. What's also notable about this film, besides the epic amount of blood and black humor, is that it was the debut from director Sam Raimi, now best known for helming the two Spider-Man films.
The Omen is scary for two reasons. One, the person responsible for doing all the damage is a cute little boy, Damien, who is the spawn of Satan. That plays against type and is therefore extra creepy. Second, the kill count is not especially high, but the way people perish is particularly impressive. You have a nanny jumping off a roof with a noose around her neck, a priest being impaled, and someone being decapitated by a plate of glass. All in all, pretty gruesome stuff.
Night of the Living Dead
The quintessential zombie film from George Romero. Zombie films are broken up into two camps. There's the old-school slow-moving zombies that are found in this and others. Then there's the recent explosion of fast movie zombies in films like "28 Days Later" and the "Dawn of the Dead" remake. Personally, I find these slower flesh-eaters to be more menacing. They just have a more methodical madness to them. Plus, as we all know, slow and steady wins the race.
This is actually John Carpenter's remake of 1951's "The Thing from Another World," and features scientists in the Antarctic who come in contact with a shape-shifting alien who assumes the identity of the people it kills. What's so scary about it is that feeling of not being able to trust anyone, even your best friend. Not to mention you have Wilford Brimley going crazy and waving a gun around, and that's always a little frightening in certain respects.
Another John Carpenter classic, about a lunatic, Michael Meyers, who escapes from a mental institution and returns home to start killing people. What sets this film apart (besides the fact that the killer is wearing a beaten-up William Shatner mask) is the eerie musical score, actually composed by Carpenter himself. Anytime that music comes up you feel your heart beating faster, and it really sucks you in.