I see nobody has put down Tokko yet, thats kinda...
sad...
Anyways! I think Tokko is awesome, but it's real short, I mean
REAL...with a stupid ending episode
...
but anyways! There's also Elfen Lied of course (which I personally don't like much) and Higurashi no Naku Koro ni/When They Cry, Blood +, Hellsing is one...and I'd also say Claymore...I haven't seen too much, but I heard it was bloody and I saw a trailer. Thats all I've got for now!