3. Alien (1979)
One of the best science-fiction films ever made and also one of the best horror movies ever made. Alien is a film that gives off the sense of complete wonder that all great sci-fi movies do yet also providing the haunting bleakness that all great horror films provide. This mesh of genres was virtually unheard of at the time and was a daunting task for Ridley Scott who was only a second time director at the time Alien was made. The cast was perfectly assembled and the story was written in such a way that there was no "main" character just one survivor who became the main character that way. Alien is an example of how to do everything right with a film. The advertising is now just as famous as the film itself with with the tagline being "In space no one can hear you scream" still being quoted to this day even though it was never uttered in the film itself. The Xenomorph is also the greatest movie monster ever conceived. It preys on everyone's worst fears while being basically un-killable at the same time. Truly a brilliant film that any director would be proud to have on their resume.