Funny tidbit, our four year old is named after an assassin in an anime. The character in question is sweet and innocent looking but dangerous when she gets started. The kiddo is holding up to her namesake.
Gamerboy likes the more depressing, but amazingly well done kind. Gunslinger Girl, Noir and WitchBlade.
I like the more upbeat colorful ones. Saber Marionette J, (I haven't finished this one yet, I love the semi poly arrangement), Kiddy Grade, BubbleGum Crisis, (the newer version) and Rune Soldier, (which reminds me of D&D).
Right now we are watch Needless, which is ridiculous and amusing.