I liked Ibitsu a lot when I read it late one night. It reads pretty much like a horror movie so I didn't get chills so much as I just liked the scariness of it (if that makes sense (=・ω・=)
I think there's also one called Jisatsu Circle that legitimately creeped me out, though I can't remember why...
first one:
http://www.mangago.zone/read-manga/ibitsu/
second one:
http://www.mangago.zone/read-manga/jisatsu_circle/
0.0 Mhz: hang on through that scientific talk in the first chapters and look forward to their little "field trip"... and read it at night... when it´s raining... and you´re alone at home...^^
Fuan no Tane and Fuan no Tane Plus: short and creepy urban legends
http://www.mangago.zone/read-manga/uzumaki/
And I've heard other works by this mangaka, Itou Junji, are just as terrifying
http://www.mangago.zone/read-manga/20th_century_boys/ What sends chills down my spine are usually psychological thrillers. This manga's chalk full of inexplicable disappearances, creepy vibes (the kind you get when something monstrous comes lurking in a peaceful setting), dark conspiracies underfoot, and an enigmatic villain to top it all off. Although it's not horror, I believe the affect is the same, and it'll have anybody biting they're nails. Takes awhile to build up to it though.
What is the scariest manga you ever read that sends chill down your spine? I am in the mood for reading scary mangas. Also please no ecchi it ruins the scariness.