Whether you are a Flickr user or not, it's worth diving into various groups and individual photo streams - similar to YouTube viewing. There are a lot of talent photographers (pros, semi-pros, regular enthusiasts and the run of the mill point and shooters) who showcase their stuff.
Recently, I came across the Library of Congress (LoC) photostream. Whether you are a history buff or not, you have to check it out. The images are compelling and really nail the time period for which they were taken. One group that captures the heart beat of America is the collection of "Women Striving Forward, 1910's - 1940's."
If you're on Flickr, friend the LoC so you can be updated everytime they post new stuff.
Photo credit: Library of Congress (courtesy of Flickr)