I liked Ibitsu, too, and found some of Junju Ito's stuff pretty good as well, but I have to say I liked the creepy ambiance of Forest of Lore as well, and Inugami and Emerging (by the same mangaka) are currently my favorites when it comes to horror. (Inugami for working in both Shinto and Judeochristian mythology as well as making for an interesting take on the "boy and his dog" dynamic and Emerging for playing up on a very real issue, an epidemic breaking out in a highly populated area that is unprepared for such an occurrence.)
In post apocalyptic Japan genetic defections are rampant and once you turn 16 years old your body starts mutating and will eventually die from it. Resources are low and people search for ways to extend their lives even if it means becoming monsters to do so.
It is not your usual horror fair considering the main character is a battle maid and there is quite a bit of sex in the storyline but it is very well done and the art is nicely detailed.
Franken Fran, Rabbit Doubt, Pet shop of Horrors, Gantz, Jisatsu Circle... eh can't think of anything else worth mentioning, I usually just stick with the psychological genre
Doubt was AMAZING! I had to sleep with the light on for like a month afterwards though. And Franken Fran is cool but I don't really consider it horror, more like just gore. Jiisatsu Circle... ugh just emotion_bigheart
I am gonna have to say Franken Fran is my favorite, even though I don't care for it and the fact that it creeps me out big time... The Horror Mansion is definitely one to enjoy to those who like horror mangas.