6. Alien (1979)
Director: Ridley Scott
Stars: Sigourney Weaver, Tom Skerritt, Harry Dean Stanton, Veronica Cartwright, John Hurt, Ian Holm, Yaphet Kotto
Depending on who you ask, Ridley Scott's Alien is either hardcore sci-fi or outside-the-box horror; we like to think of it as a classic. We're guessing Scott would prefer that branding as well.
Essentially a haunted house story set on a spaceship, and with a homicidal alien in place of a ghost, Alien meshes the two genres together so well that it defies narrow-minded categorization. Sigourney Weaver, in her breakout role, runs shit as the heroine, Ellen Ripley, one member of a crew trying to survive a terrifying, quick, and bloodthirsty alien's rampage on their ship.
Under Scott's watch, Alien packs a plentiful amount of genuine scares, palpable tension, and dazzling visual effects. Speaking of the FX, the alien's design, credited to the excellent H.R. Giger, is hands-down the freakiest of its kind; with a long, jai-alai-racket-shaped head and Velociraptor-like arms and legs, the film's monster is the stuff of intergalactic nightmares. It's also the benefactor of one of cinema's all-time great taglines: "In space, no one can hear you scream." Too bad the people watching Alien with you can.