Birdy the Mighty Decode (1 and 2)
Fullmetal Alchemist (preferably the original/Brotherhood)
Death Note
Mirai Nikki
Zetman
Kaiji
Hikaru no Go
Akane-chan Overdrive
And I like Yu Yu Hakusho to some extent.

Based on these, could you give any recommendations? (Please, no Naruto, Bleach, or Vampire Knight)
Whoops, forgot to mention. Already read/watched Elfen Lied and love it. Thanks for the suggestion though ^^