I can't think of any off hand, since I don't read too many books with sex scenes. The best sex scene I ever recall is when Ayla has sex with a non-nonenderthal in the series of books about life during the stone age. Alas, I can't think of the series or the author at the moment, but I'll do some research.

Okay, here it is:

The Complete Jean M. Auel Earth's Children Series Six Book Set [Clan of the Cave Bear, Valley of the Horses, Mammoth Hunters, Plains of Passage, Shelters of Stone, and Land of Painted Caves] Mass Market Paperback – Unabridged, January 1, 1990
by Jean Auel (Author)

Check on some later LaVerle Spenser romance books. She might have some. I like her as a romance writer.