The Library of Congress has a stupendous, enormous photo gallery called "America from the Great Depression to World War II: Color Photographs from the FSA-OWI, 1939-1945," which includes gems like this image from 1941, "At the Vermont state fair, Rutland, 'backstage' at the 'girlie' show." Unfortunately, the organizational back-end for this is so primitive (especially in comparison with modern image-sharing and organizing sites like Flickr) that it, too, seems to hail from 1939-1945, making the site a real pain to navigate and use.
(via We Make Money Not Art)
Update: Alex sez, "I'd like to recommend just as highly a collection of Edward Curtis photos also housed at the LOC, an extensive set of ethnographic potraits, stark and beautiful, captured in another time. Although these aren't in color, the collection is just as stunning, and I would encourage your readers to spend a few minutes looking back through them. They remind me of the many months I spent poring over The Smithsonian's Bureau of American Ethnology Annual Reports (a congressionally mandated compilation of studies covering various Native American tribes, spanning nearly five decades) as a student, reading in books what I could never see in person."
Update: Kirby points out that the Cushman collection sports 15 pics of Disneyland taken on March 26, 1959.