Pic related is mine. Such a solid movie. From being a critique of consumerism to racism, to an action movie, to comedy at some points. And while it might not be scary in the traditional sense, the opening scenes detailing the chaos around a news station trying to remain calm during the end of the world are done pretty well and set the mood for surviving the apocalypse.
Alien (1979) is not only my favorite horror movie, but one of my favorite movies in general along with Aliens (though that's more of an action film).
I've only seen The Shining once. I watched it alone in the dark in my dorm room at like 2 in the morning. Probably the scariest film I've ever seen and I didn't sleep at all that night. I still remember every scene years later.
The Blair Witch Project is great because nothing really happens during the film's 2 hour run time. But then the last ten minutes are just fucking nuts. The audio not synching up because the camera is in one room while the mic is in another creates such an eerie effect with so much tension.