The National Archives, the UK government’s official archive, containing over 900 years of history have made a selection of their images available through Flickr to give some idea of the material they retain.
There are some fantastic images ranging from Jane Austens will, to The Big Three at Yalta (Churchill, Roosevelt & Stalin), Medieval manuscripts to Whitley Bay posters, maps, plans, seals & artifacts and all are in the Creative Commons with no known copyright restrictions. What about the US National Archive phototream? An amazing collection from the American Civil War to photodocumentaries of everyday life in the 1970′s.
You can comment on the pictures and make copies of them so why not have a look?