Naruto is too tight!

Higurashi no naku koro ni (as someone else has mentioned)

Definitely Corspe Party, idk I couldn't even get myself to finish watching it.
I enjoyed watching Elfin Lied tho, idk I watched an episode when I was younger by accident and when I found it again, I could look past the gore and I liked it lol

I looked back at this and I have a few to add.

-Sundome - Made you cry in pain
-Aku no Hana - psychological content heavy
-Akumetsu

For me, it would be:

Highschool of the Dead
Lucky Star (this anime was too weird for me...)

Death note. I was very disturbed by the fact that it couldn't be real