Just Manga

The next Kuroshitsuji volume comes out July 19th 2011 in English. (That's volume 6)
 
My personal favourite manga that fall under your categories are...
Ghost Hound:
It's essentially a murder mystery, expect these three young boys are able to step out of their bodies and explore the 'Spirit World'. They soon discover that the answers to their traumatic pasts lie within this world. Then the whole natural and supernatural world is thrown out of whack. It's amazing. The manga only has like 2 volumes, and I haven't read it so I can't vouch for that. The anime, though, is amazing and I highly suggest it.
 
Parasyte:
A young man is infected with a strange alien parasite in his right arm, but others aren't so lucky as their brains are taken over and their only drive is the destruction of the human race. Super awesome.
 
D Gray Man:
Allen Walker is blessed with the gift of Innocence, allowing him to fight against weapons, Akuma, sent to destroy humans. But things would be all fine if he wasn't up against the Millennium Earl and his posy of superhumans. One of my favourites.
 
Chrono Crusade:
Rosette fights to destroy demons and evil in the world. Along side her is a demon, Chrno, who is set on fixing the wrong he has done in his life. Really an amazing franchise.
 
Darker Than Black:
In this world there are contractors, and humans. Contractors have been given supernatural powers, such as gravity control, or teleportation. But in exchange they must pay a price. Hei is a Contractor, but he doesn't have to pay a price. The manga and anime follow him and his dangerous espionage and assassination missions. Another one of my favourites.
 
EDIT:
The Nightmare Inspector:
Hiruko, a baku, cures people of their nightmares by entering them, and solving the mystery behind them. Really good, but dark and twisted. I love it.

@fehafare: Maybe your read the japanese fan-translated one?

@fehafare: Read "Freazing", it's better to try something new.