In general I tend to like horror, investigative stories, believable sci-fi, slice-of-life literary stuff, and black comedy.
Kurosagi Corpse Delivery Service is also one of my favorites, and from what I can tell, we like the same kind of manga in general. So I have a couple of suggestions.
First of all I'd second (or third, or whatever)
Mail. Written and drawn by the artist for KCDS, it's creepy and effective, if a bit repetitive.
For horror, I highly recommend the various
Mermaid series by Rumiko Takahashi.
She's more well known for the kind of manga you avoid, but trust me, this is as truly horrific as any manga I've read. A lot of the horror manga I've sampled is full of histrionics and isn't actually scary at all, and isn't to my personal taste because of it.
Drifting Classroom, for example, is 200 pages of people shouting hysterically at each other.
Mermaid is a great deal more subtle.
For realistic science fiction I'd recommend taking a look for
2001 Nights:
It's a very non-exaggerated look at what might happen if humanity develops the ability to travel long distances through space.
Lastly, I'd recommend checking out some of Taiyo's Matsumoto's work.
Harder to characterize (and that's part of the appeal), Matsumoto has done a few things published in English:
No. 5,
Black and White (also called Tekkon Kinkreet) and
GoGo Monster, all different and all fantastic.
Lots of other great recommendations here. I would like to check out
Saturn Apartments myself.