Ok, here are mine.
Not sure how many people know about this one but Hibiki's Magic is a really great manga about, to put it in very basic terms, a girl who ends up becoming a teacher at a magical academy and the various shenanigans that happen to her. It looks really cute(thanks to the art), but the story can be quite bittersweet at times, especially the side story at the end of volume 1. Only 2 volumes have been produced, and the first one came out in 2004, so this is unfortunately an unfinished series.
Kurozakuro, also a manga, is about a high school student who's never hurt a person in his life becoming a monster that loves the sight of blood and the taste of human flesh. When I read volume 1, I couldn't put it down; it's really good.
Millennium Snow, by the author of Ouran High School Host Club(Bisco Hatori), appears to also be an overlooked series. It's a cute shoujo manga about a vampire who knows the pain of living forever(one notable line: "Can you understand the horror of living for a thousand years?!") and a girl with a heart condition who could die at almost any time. It's pretty comedic, but it also has some serious parts. Bisco Hatori worked on it before Ous Host, but she put it on hold when Ous Host got popular, so only two volumes were released. She
just released volume 3 in August, which made me pretty happy.
As for one off the top of my head, Aoi Bungaku is an interesting little series.
On a random note, I've always wanted to get around to watch Aoi Bungaku because I like No Longer Human by Osamu Dazai and the short stories of Ryunosuke Akutagawa, especially
Mandarins. I know it isn't anime or manga, but if you ever get the chance, read
Mandarins. It's a short story well worth your time.