IFC compiled a list - unlike everybody else's list this year - regarding scary movies.  Sometimes, as you're watching a comedy, science fiction, or drama flick, they pull a fast one on you, and the next thing you know you're jumping out of your seat.  For instance, the "Large Marge" scene from Pee Wee's Big Adventure.

"When they finally pulled the driver's body from the twisted, burning wreckage," she groans. "It looked... like THIS!" Suddenly, Nunn's face is replaced by a ghoulish claymation head, which howls at Pee-Wee with bulbous bug eyes, serpentine tongue, and enormous, snaggle-toothed maw. An understandably frightened Pee-wee asks to be let out at the next truck stop, where he learns that he couldn't have gotten a ride from Large Marge; she died in the very accident she described, ten years earlier.

See all 25 examples at IFC.  (Photo: Warner Bros.)