For me, Takemiya Jin, Morishima Akiko, Hajime Mikuni, Fujieda Miyabi and Amano Shininta are at the top for original yuri; Personal Colour, Pikachi, Millet Soup, Mikami Komata, Fukutarou and Yohane really do it for me for doujins, and I like Mitsuru Adachi, Kozue Amano, Hitoshi Ashinano and some things CLAMP does when it comes to non-yuri stuff.
Oh, and there's really only one yaoi I really like, and that's Mainichi Seiten by Sugano Akira and Ninimiya Etsumi.