One of the many projects that emerged from the aborted attempt to do Dune in the 1970s, Alien still stands as the pinnacle of sci-fi horror. Despite being almost 40 years old, the movie still holds up well as a vision of the future.
The premise is right out of Halloween or Friday the 13th, isolate a mixed group of people somewhere and introduce a deadly killing machine. Sit back and watch the magic happen. In this case, the mixed group is a team of workers who intercept a distress signal on their way home through space and decide to investigate. Once at the source of the distress, they pick up a new passenger in the form of a slimy little creature who has attached itself to one of the crew's faces. You've all seen the scene with the alien bursting out of the man's chest. It quickly grows up and causes more problems for the crew. The remaining crew gets picked off one by one and even has to deal with an internal threat in their ranks.
This is a great slow-burn horror. The first hour is mood setting and character development. By the time the alien is moving through the shadows and killing the crew, you have gotten to know and even like a few of them. Also, like Jaws, this movie works because of how little they show the alien. Designed by H.R. Giger and his nightmare visions, the alien is all curves and points but the less we see of it, the scarier it looks in our minds. Great performances by Tom Skeritt, Sigourney Weaver, Ian Holm, John Hurt, Yaphet Kotto, and Harry Dean Stanton really bring the danger to life.
The sequel might have kicked more ass but the original is still my platonic ideal of horror in space.