15. High Tension (2005)
Spoiler Alert! The male killer we see throughout the film is actually a figment of Marie's imagination. She's the one doing all of the slicing and dicing. It's one of those improbable endings that explains away the inconsistencies by stating that everything was seen through the eyes of a crazy person. The same thing happed with Glitter.
14. The Wicker Man (1973)
Spoiler Alert! The story of the missing girl was made up to lure the cop to the island so that he could be sacrificed to the inhabitants' pagan gods in a burning "wicker man." Weenie roast at 8:00 by the goat's skull!
13. The Orphanage (2007)
Spoiler Alert! The ending is open to interpretation, but from what I gather, the house is haunted, but the "ghost" that the mother sees is in fact her son dressed as the bag-headed ghost boy. After she punishes him for misbehaving, the son puts a bag on his head, attacks his mother, then gets scared and runs to hide in a secret room accessible through a closet, where he falls down and dies. In the mother's haste to find him, she inadvertently knocks over a post in the closet that blocks the secret passage, preventing the son's body from being found.
12. Diabolique (1964)
Spoiler Alert! The husband isn't really dead. He and the mistress plot to make the wife think he's dead, then scare her into having a heart attack.
11. Black Christmas (1974)
Spoiler Alert! Five years before When a Stranger Calls, Black Christmas originated the "crank calls coming from inside the house" routine and put it where it should be: at the film's climax. Granted, this revelation isn't terribly surprising, since we see the killer systematically picking off sorority figures inside the house, but it was influential, and the film's final twist is that the man who dies and is assumed to be the killer turns out not to be the one. He's still INSIDE THE HOUSE.
10. Angel Heart (1987)
Spoiler Alert! Harry is Johnny. Johnny killed the real Harry and assumed his identity, then was drafted into the war and got injured, requiring extensive facial surgery and causing amnesia -- so he doesn't realize who he is, and no one recognizes him. Furthermore, Harry/Johnny is the person killing all of the people, under the influence of the man who hired him...Satan himself! (who looks surprisingly like Robert De Niro)
9. The Skeleton Key (2005)
Spoiler Alert! The spirits of the two servants are in the bodies of the old couple. Well, originally, the old man held the male servant's soul, but it was transferred into a young lawyer, while the spirit of the female servant is transferred at the end from Violet into Caroline's body. The film ends with Caroline's soul and that of the young lawyer occupying the old couple's bodies, both incapacitated and mute, and the servants having new young bodies.
8. Seven (1995)
Spoiler Alert! The killer offers to take Mills and Somerset to the location of the sixth and seventh victims. When they arrive at the barren outdoor location, a delivery van drives up and drops off a box containing Mills' wife's head -- thankfully, not C.O.D. The killer confesses that he killed her because he was envious (the sixth sin) of the Mills' family life. Mills, using his wrath (the seventh sin), then shoots him dead, all according to the killer's plans.
7. Friday the 13th (1980)
Spoiler Alert! Is Jason responsible for the deaths? No, it's his mother, Mrs. Vorhees, wearing a fashionable sweater. But wait, there's more! The last remaining counselor, Alice, kills Mrs. Vorhees and goes for a gentle float in a canoe -- at which point Jason's decaying little boy body jumps out of the water and drags her under. The police eventually pull her out, and Jason is never heard from again...except 11 or so more times.
6. The Ring (2002)
Spoiler Alert! Rachel does all of the grunt work to find out that Samara's body is lying at the bottom of a well and then even goes down there to retrieve it -- thus, by all normal movie logic, freeing the restless spirit from haunting people through video tapes and prank phone calls. However, as Rachel's psychic son so effectively points out, Samara is evil, and Rachel has succeeded in freeing her spirit to kill at will. Nice one, Mom.