Since Vanessa Chase has just been taken, I'm going to vote for what I consider to be the hottest one-timer I've ever seen. In his controversial Buttman Confidential, John Stagliano introduced a really hot short-haired gal by the name of Michelle Derriere, featuring her in three scenes (a dance tease/handjob, a dildo scene, and a full hardcore scene with "Hatman"). Despite her ridiculous stage name, she has stuck with me over the close to 10 years now since Confidential came out. And to this day I've yet to find of any other work she's done.
Making matters worse is the fact that Evil Angel for whatever reason doesn't to release the film to DVD, and to my knowledge hasn't even included her scenes on any best-of compilations. All I've ever found of her is a reference (and, for a while, a few pics) of her promoting Confidential at a porn convention, and she's also referenced in a Village Voice article on porn. Otherwise it's as if she dropped off the face of the earth.
If life were fair she would have become one of Buttman's recurring ladies like Nina Hartley or Krystal Lynn.
As I discovered when I put out a WEHT thread about Michelle Derriere, there is virtually nothing on her online now, hardly even a picture.