It hasn't been updated since his death in 2004, but Richard Avedon's professional web-site is quite good, with many images to mull over.
Time's retrospective of Avedon's work includes Dovima, which is exquisite.
Also worth a gander: PDN and Kodak's site of Avedon's The Sixties. This image of Alice Cooper and Frank Zappa is particularly good.