I don't know their names, but there are these three gay pornstars from the 90s that were in alot of movies, but they were so ugly and flaming that I can't believe that anyone would do them without pay. Most of the actors they performed with had hard times getting hard and I can't blame them.
I think a younger Ron Jeremy wasn't so bad, but obviously the years haven't been kind to him.
As far as straight performers, I'd have to say any actor who clearly didn't deserve to be fucking those chicks (i.e. fat, old or both) and this chick Candy Cotton with the most hideous boob job in the known universe.