US National Archives
Nara: Picturing the Century: A New Century
This site has a series of photographs of different areas in the United States during the beginning of the 20th century.
Library of Congress
Loc: Progressive Era to New Era, 1900 1929
This website defines and explores the Progressive Era and various aspects of American society during that period of history. It contains fairly simple text and several images.
Then Again
Then Again: Web Chron: The Progressive Era 1879 1920
Visit this site for a chronological listing of the important events that occurred during the Progressive Era. Some events listed have links to further information.