Traci Lords went mainstream after the big scandal. Not that she made it to any great movie roles, but she was in a few movies and TV episodes.
Sasha Grey of course was in this last season of HBO's Entourage, though playing herself. Was also in Steven Soderbergh's "The Girlfriend Experience", a movie from 2010.
But anyway, to cut to the chase for porn stars who've appeared in mainstream movies:
http://en.wikipedia.org/wiki/List_of...instream_films
Now, any that had a major career in mainstream? Not really.