Suzuki Tsuta -gay- First two chapters of Akanai Tobira are amazing, she made such a plain boring guy so hot to me (it may also have something to do with the fact that I think Dangerous Pleasure's typesetter for this is amazing, or he really is the most endearing uke ever). She's one of the only yaoi mangaka who can write a whole volume and not have any sex in it until the very last pages and I would still be engrossed (which is what she did in Sangen Tonari no Tooi Hito). Oh and I really love her portrayal of having a gay relationship in general.
Yamane Ayano -gay- Her sex scenes are amazing. Crimson Spell looks like a stereotypical fantasy-genre yaoi but I highly highly recommend it. And there's always Viewfinder, so much great sex in there.
Naono Borha -gay- No yaoi-mangaka list is complete without her. And it really helps that her entire massive body of work is just so wonderfully accessible in English. Her coverage of different kinds of couples very notable, from 'normal' people to large social or economic gaps, age (usually meaning 'normal' aged people and middle-aged men), disabled peoples, fantasy-elf-like beings, traditional Japanese with top-knots, she does everything. And she makes 50 year old men hot which says something.
Maki Murakami -gay- Holy shit this girl has balls. I love her gritty, HARDCORE doujinshi. If there is a God and Haruhi is that God, the reason why Haruhi created Maki Murakami is so she could create manga so she could create doujinshi of her own manga. Gravitation and Gamerz Heaven serve no other function than to be made into doujinshi by their creator. The MurakamiUltimate and Gamerz Heaven doujins are a historic event for yaoi, what with their internal cum shots (which I've never seen anywhere else in yaoi) and fisting anuses and pissing in anuses and pissing in mouths and huge gang bangs and oh yeah slashing open people's stomachs and killing people while you're fucking them. It helps that she's gotten much better at drawing since the original publication of Gravitation, and she's not guilty about drawing yaoi now that her kids are older. She's still not the best artist in the world but she's gotten so good at drawing the look on a guy's face as someone shoots their load in their mouth.
CJ Michalski -gay- I guess by the name this person's half? Anyway, her stories are very through and through Japanese as much as anyone, and she's good. I love her, I wish more of her works were accessible in English. Maybe I could scanlate?
Naruko Hanaharu -straight- I don't like it when she draws stuff with massive tits. I think I like most of her stuff with normal-sized tits, and I like that she has a big body of work to pull from. Turns me on so thumbs up.
Other notable mangaka are Yoshinaga Fumi (Antique Bakery), Sakuragi Yaya, Itsuki Kaname, and Nakamura Shungika (Hybrid Child, Junjou Romantica). And everyone else I know are pretty much just one-hit wonders. All the hentai and yuri I like are also one-hit wonders, so no one made my list.