Yoshitoshi Abe is one of my favourites. I love the sketchy quality to his work, how his drawings look more like something you'll see in traditional art, and not a manga/anime.
Then I've got my three favourite manga-ka artist's.
Kaori Yuki, Mokona Apapa (Clamp) and Yoko Matsushita.
All three are women, and all draw my three favourite manga(s) of all time. I've got artbooks from each of them, and they are all so beautiful.