Tom Wesselmann's Dali-esque "Mouth #8" (1967)
Salvador Dali's Manet-esque "Playmate After Rokeby Venus" (1966), from "The Playmate as Fine Art" feature of January 1967
A 1953 portrait of Marilyn Monroe riding in the back of a convertible. The background was cropped out when the image appeared on the cover of the first issue of the magazine.
Stephen Wayda's 1993 portrait of famous Canadians Pamela Anderson and Dan Aykroyd; sexy because coneheads are phallic.
Herb Davidson's portrait of Hefner, not sexy in the typical Playboy manner, more so in that "handsome man smoking a pipe" manner.
This makes me really curious about the Hustler art collection—which I suspect doesn't exist. But if it did, it would definitely be full of Nan Goldin, Carolee Schneemann, Alvin Baltrop and so forth. A much more interesting auction, really.