Takemiya Jin is my personal favorite yuri mangaka. Morinaga Milk, Otsu Hiyori, Akiko Morishima, Minase Ruruu, Eban Fumi (for Blue Friend), Mikuni Hajime, Hakamada Mera, Rokuroichi, Momono Moto, Amano Shuninta, and Aoi Hana (the author, not the manga) are all quite decent though.
As for non-yuri mangakas the only one I'd actually put on my list of favorites is Junji Itou since he's the only horror author (for both books and mangas, not even going to bother touching on games or, especially, movies) who I consistently enjoy reading, even when what he's writing is blatantly supernatural which I tend to hate because it devolves into more horror-themed fantasy at that point than actual horror with the majority of authors.