You can have Saw and Hostel. When it comes to movies that invade Flickgrrl's nightmares, few are as unshakable as Night of the Living Dead (1968), George A. Romero's unexpectedly potent (and lyrical) account of flesh-eating zombies stalking the living in and around Pittsburgh. In his landmark monster film, Romero introduced the unkillable and insatiable threat. Particularly creepy about the movie shot in contrasty black-in-white (with Bosco chocolate syrup used to simulate blood) was that when the film ended, the terror didn't.
(Because the undead were insatiable, many interpreted them variously as a metaphor for consumerism and capitalism; just as many saw the zombies as symbols of the U.S. soldiers in Southeast Asia preying on the Vietnamese.)
For better and worse, Night of the Living Dead (itself inspired by Richard Matheson's I am Legend and Herk Harvey's eerie 1962 flick, Carnival of Souls) John Carpenter (Halloween) and Night Shyamalan (The Happening), Danny Boyle (...28 Days Later) and Cormac McCarthy (The Road) who each appropriated the trope of the handful of good guys barricaded in a house while the zombie (or zombie army) figured a way to storm the fortress. (Prior to Night of the Living Dead, his feature debut, Romero had filmed shorts for the PBS kiddie show, Mister Rogers' Neighborhood.)
Romero's latest, Survival of the Dead, opens Friday, a prospect that occasions Flickgrrl's fond, albeit unsettling, memories of the Dead movies, which also include Day of the Dead (1975, the one with the army guys and the female scientist in the bunker as zombies lie in wait) and Dawn of the Dead (1978, the one where the living -- as opposed to the living dead -- have created a commune in a shopping mall).
Much as Flickgrrl likes the Dead series, her favorite Romero film is the underknown Monkey Shines (1988), about a capuchin monkey placed in the home of a quadriplegic to serve as his surrogate hands. Before long, she becomes his surrogate id. Yikes! Your favorite Romero? Alternatively, the film that scares you the most?