My top3 are Higurashi, Elfen Lied and Mirai Nikki. @ZELIMAN13: tell me when you're finished Shiki.
I myself think it's a horrible anime and not horrorfying at all in everey single aspect~
Closest thing to horror I've watched as far as anime is concerned is Attack on Titan. The genre isn't something I really going hunting for but I may go through this thread and watch some of the stuff you guys mentioned
has it's moments. Not like corpse party or higurashi, because first it's an actionanime and secondly there is no innocence or otherwise cutnessfaktor in the anime, that would hype the impact of violence. The big plus of Hellsing ultimative is that the characters are wicked and reckless, therefore there are several scenes painfully shocking to watch. http://www.anisearch.com/anime/3391,hellsing-ultimate
Shinsekai Yori (2012)
is a dramaanime deceivingly not for thin-skinned personalities and has given me sleepless nights. The settings and storylines are so mysterious, twisted and dark. I think it's a one-of-a-kind anime like higurashi and for horrorfans it's time well spend. http://www.anisearch.com/anime/7640,from-the-new-world