AlanBarr:
Coming across a spanking reference unexpectedly is a special sort of pleasure which it's impossible to replicate with a spanking story.
Agreed. Any unexpected spanking in mainstream media is usually better than one where you expect a spanking.
Here's a few from memory:
The Warlock In Spite of Himself : the inexperience queen want to lead her troops in battle, which would have been terrible, so the "warlock" said that they had to make sure she couldn't sit astride a horse. One of her supporters was outraged, thinking the "warlock" meant sex, but it was clarified that he meant spanking. One bare bottom spanking later and the queen couldn't sit on her horse.
Arrows of the Queen (Mercedes Lackey's first book) includes a "country spanking" on the butt of the spoiled princess (or maybe it was just the threat of one).
Sharon Green - started off as mainstream sci fi/fantasy with some spanking, dropped the spanking at the insistence of her publisher, now self publishes her books with spankings in them.
Piers Anthony - several of his books have cute teenage girls getting spanked - or being threatened with spanking.
Off handed mentions of spankings in countless old children's books - including James and the Giant Peach.