For me personally it's gotta be Fullmetal Alchemist: Brotherhood. Such a fantastic story, and one of the few shows I've gone back and re-watched several times. Even got my gf, who is not into anime, to love the show too, though her favourite remains Avatar The Last Airbender.
Honorable mention to Pantheon too, that one kinda broke me for a couple days. Just wish we got a bit more of the show so season 2 didn't have to be as rushed.