Yeeek! I love so many. <3

Loveless, both the anime and manga
Yami no Matsuei / Descendants of Darkness, both the anime and manga
Ouran High School Host Club, only the anime. I thought the manga was disappointing. :\
Yakitate! Japan, the manga; I haven't seen the anime. XD I should go see it.
Fruits Basket, both the anime and manga