In terms of movies, I've watched most of the "big name" horror movies: The Ring (meh), The Grudge (1 was great, the rest were terrible), the Saw movies (starts off great and declines), Event Horizon (deserves its reputation), The Conjuring (best horror movie I've seen in the past 3 years), The Babadook (really cool movie)... but nothing, NOTHING has come close to beating Rec for me.
Rec was made in 2007, and is a Portuguese foreign film. I'm not big on foreign films, as I often feel the subtitles distract from the immersion, but DAMN this movie was good. I've never been as legitimately scared of a movie as I was when watching Rec. It's short (only like 80-90 minutes) and technically falls into the zombie plague category, but to everyone reading this: do yourself a favour. I can't explain why it's as good as it is, and the Hollywood remake (Quarantine) was terrible imo, but the original... man. An absolute gem.