A few are Henri Cartier-Bresson, Robert Frank, Sebastião Salgado, William Eggleston, Stephen Shore, and Lee Friedlander
To elaborate at bit on a couple of the folks named above: HCB and Frank got me fascinated with photography before I ever owned a camera, and a Friedlander traveling exhibition I saw a few months back at Cleveland Museum of Art totally blew my mind and made me completely reevaluate anything I had ever thought of in terms of what made an image work.