Hunter X Hunter
It starts off a bit kiddy like, but gets really dark later on. It's my favorite anime ever.
I also really liked Engaged to the Unidentified, Say "I Love You", and My Little Monster, but they're kinda cute animes so I'm not sure if they'd be your style.
Inuyasha was really good! I loved it so much!
Durarara was good too, but I only really liked the first season.
Black Butler was good too, but I've only watched the first season of it.