The Footnote site is a rich source of primary source documents and images. The majority of the files are free although some do require a subscription. The collection has an American emphasis yet there is quite useful material for students of history in Australia.
I have found the documents from the Japanese photographic archives recovered after WWII to be particularly interesting since my father was a guest of the Japanese following his capture in Malaya by the Japanese army in January 1942. A number of the photographs in the Japanese category were taken in Singapore. A tip of the hat to Larry Ferlazzo for his post pointing to this site.