A scanned version of Henri Cartier-Bresson‘s long out of out of print and fantastically expensive photography book, The Decisive Moment, is now available online at e-photobooks.
Quoth the Wikipedia:
Cartier-Bresson is considered to be the father of modern photojournalism. He was one of the first serious photographers to shoot in the smaller 35mm format, and is commonly considered the undisputed master of candid photography using the 35mm rangefinder camera. He helped to develop the "street photography" style that influenced generations of photographers to come.