Dorothea Lange is one of the iconic US photographers of the past century and, if I may add this personal comment, one whose work I actually enjoy and admire (unlike, for example, Ansel Adams’s work that I find so utterly boring and vastly overrated). There is a fairly large selection of her work online: this page has lots of variations of the famous “migrant mother” photo shown above. I bet you never noticed Dorothea Lange retouched it (oh, the horror for all those photo “purists”!). And this page has lots and lots of photos.

PS: I find the subtitle of the official site - “Photographer of the People” - quite odd. Sounds like late 19th century labour movement to me.
(all links from wood’s lot)