Garry Winogrand - it may be through sheer volume, but some of his photos have left indelible marks on me. Can't remember the titles, but my favorites are:
Photographer in Central Park
Couple with Chimps
Black deliveryman juxtaposed against white businessman
The one where all the men are looking at the girls
and many others...
Clyde Butcher - for being a master of the landscape. Absolutely amazing images.
Dorathea Lange, Ian MacEachern, Emil Schildt, Dan Burkholder are other favs.