I would say FLCL has pretty kickass style, but...you've probably seen it.
I've always liked the art of
Vision of Escaflowne. If you haven't seen that series, I'd recommend it. I've always liked the look of
Last Exile, a show about people who fly planes and airship sorta stuff around. I've heard Kino's journey has some pretty amazing artwork, though the main character looks sorta weird to me (never seen it). Hmm, it's sorta interesting to me that all three of these shows are at least a little steampunk.
And I really like One Piece's weird character art

I have a soft spot for One Piece.
Erm, I think the guy who did ghost in the shell has a pretty big following as an artist. But I don't know his name, and I haven't even seen his work -_-