(photo: Brian Ulrich, Magnum)It is not possible to consider the history of photography without mentioning the Magnum group of photographers, a cooperative of many of the most successful documentary photographers in the world. Established in 1947 and still going very strong today, you can meander through an amazing array of images if you've got the time:
Magnum Photography Web Site
A nice aspect to the site is a listing of updated photography contests and awards that you can apply for. A good way to stay motivated and to get your work out there. This is a big one, due Sept 30th (perfect timing!)
Magnum Expression (Documentary Photography) Award