Uzumaki

I think I've read everything Junji Ito and it's really hard to choose, but I love the whole spiral obsession element. I bought a hardcover collection of Uzumaki in April for my boyfriend and I still don't think he's read it (how hard is it to read a comic book?). Junji Ito also got me into Kazuo Umezz and other classic horror mangaka recently.

I am a Hero

Hands down my favorite ongoing manga. Has forever altered the zombies that appear in my nightmares though, I liked it when they didn't talk.

Number 3 is probably Berserk, although I haven't kept up with it as much because it's constantly on hiatus. Definitely read it if you haven't, but skip the anime adaptations because the best thing about it is the artistic detail in the manga. Skip if you can't stomach gratuitous violence and adult content, because it is excessively so.