Although it doesn't match up to some of the classics on here, The Descent was one of the most impacting scary/horror movie I'd seen in recent years. I got it thinking it was The Cave which had horrible reviews. With a few family members joined in audience, we expected a late night laugh. However, it turned out entirely different. I don't get scared or affected by movies much but this one did it. It's likely so because I once got stuck exploring a cave mostly alone which would have been even more horrible had I not managed somehow to suppress panic and get myself unstuck and on my way.

Alien and The Thing are my favorites to echo above statements. It would be amazing to have seen them in theater when they were released and not yet known to the world (same for The Exorcism).

I was disappointed with the Tunnel. Although pretty good, it fell flat for me. I much prefer REC (the Spanish original) as it was pretty effective, especially the ending, for found footage film.

I just want to say that Rosemary's Baby was ridiculously well done and it deserves a place on such a list. And Suspiria... Just a gorgeous film to look at.

Paranormal Activity, slow building tension and very simple effects so that imagination does the rest, good job. And The Thing, obviously