http://learning.loc.gov/ammem/collections/finder.html
American Memory: Historical Collections for the National Digital Library
From the Library of Congress, this must-see site grows daily. Click on the time-line for the appropriate era.

http://xroads.virginia.edu/~1930s/home_1.html 
University of Virginia's 1930s Project 
Examines the years between Black Tuesday (1929) and the bombing of Pearl Harbor (1941), through the film, print, radio, and design of the era.

http://newdeal.feri.org/
New Deal Network 
Covers the era of people who lived during the Great Depression into the early 1940s. Stories, radio broadcasts, and more. 

http://www.fiftiesweb.com/fifties.htm 
Fifties Web 
Recommended by the History Channel, with good links to music and television of the '50s.

http://www.lib.virginia.edu/speccol/exhibits/sixties/
The Psychedelic ‘60s