Professional Photographer magazine published a great list of the 100 most influential photographers of all time.
Six photographers from the list are below along with samples of their work, taken from Google Images:
Richard Avedon (1923-2004)
W. Eugene Smith (1918-1978)
Guy Bourdin (1928-1991)
Henri Cartier-Bresson (1908-2004)
Diane Arbus (1923-1971)
Elliott Erwitt (1928- )