For anyone who has yet to see it, I quite love the Library of Congress' flickr photostream. What a fantastic way to make historical images readily available! It refreshing to have free access to communal history when so much in today's world is forbidden by copyright and ownership.
From the Titanic, to the Suffrage movement, to the building of bridges, to the pioneer days, there are so many fantastic moments captured on film to be searched through. Go check it out!