i know it's not really anime but god it looks so awesome...(yayyy KOTOR MMO)
http://www.youtube.com/watch?v=jylNo5tTiSg
... also i recommend Shin Megami Tensei: Imagine Online and Sword of the New World/Granado Espada which is pretty anime-ish and has a pretty fast-paced cool combat system
ohhh and also there's an anime like 3rd person hack and slash mmo on 360 or pc called Phantasy Star Universe. I tried it its really fun! if you have a 360 there's a free demo thats online, except the demo is nothing compared to the full version. you can go do dungeons and bosses and stuff or you can hang out, customize your room, upgrade weps. only bad thing is it costs $10 a month for the full version+another $10 for the expansion which is a must have if you plan on playing online. so if you enjoy the demo and can afford the monthly fee its definatley a good choice!