"Pleasant unpleasantness"

...or "unpleasant pleasantness." It's something I invented to use when I need to come up with a new phrase. I found myself using similar descriptions over and over, and getting stalled in the middle of a heated scene.

I take out my thesaurus--again with the thesaurus!--and I jot down synonyms for "pleasant" or "pleasure" or words like it. Examples: delight, please, thrill, enjoy, gratify, joy.

Then I jot down synonyms for "unpleasant." Examples: torture, suffer, ache, torment, anguish.

Combining one from column A and one from column B, you get:
delightful torture
thrilling torment
joyful suffering

It works the other way around, too:
anguishing thrill
aching delight
tormented gratification

Excercise:
When your characters are on the plateau before orgasm, give them some "pleasant unpleasantness" or "unpleasant pleasantness." They will be achingly grateful, and delightfully anguished.