I'll just concentrate on some lesser-known ones (hopefully no dupes - I know some mangaka use different aliases):
(wow! he practically justifies a Fakku subscription all on his own!)
- Kitakawa Touta (if you like his art style, then be sure to check out his non-hentai work Seishun Pop - dark and ecchi towards the end)
(like how he tends to focus on older women - refreshing given the glut of schoolgirls in hentai)