This is another hot one. The progression of the man's Dominance, and of the girl's sexual training and submissive conditioning, are both very believable.
This is a long, well-written story by a very good author. It's not so much a stroke story as it is a well-written story that explores long term D/s (Dominant/submissive) relationships.
Topcat's stories all involve black bull dominance. Most (including this one) are incomplete. I think his wife caught him and forced him to stop writing.
Silkstockingslover is a prolific erotica author. Her stories are very well written, and usually involve lesbian D/s. While her works appear on many forums, the ones here are well worth reading.
No way I could make a list like this without including at least one story by Stepdaddy. He's got a bunch of good ones. I'm limiting myself to one for this list.