At Christie's at Rockefeller Plaza in New York important photographs from the 19th and 20th century will be auctioned. You can find at this auction first class prints by e.g. Irving Penn, Ansel Adams, Eugène Atget, Man Ray, Diane Arbus, Robert Mapplethorpe, Helmut Newton, Bill Brandt and Henri Cartier-Bresson.
To give an impression about the current value of some photographs in the market of photography collectors, you can find the highlight of the sale below. It is Diane Arbus' well-known photograph named Identical Twins, Roselle, New Jersey (1967). It is estimated to be sold for $ 250.000 - $ 350.000.
Although Diane Arbus' pictures are very nice, I'd rather enjoy making pictures myself. It is a much richer experience.
Update October 11, 2010. From the auction results I understand that Diane Arbus' Identical Twins, Roselle, New Jersey was not sold this time. On a comparable auction at Christie's back in 2000 the picture (or a similar one) was sold for $ 270.000.