PRIMARY SOURCES: IMAGES
Library of Congress' American Memory project includes 65 collections containing photographs
Life magazine photo archive hosted by Google with Browsing Capability
New York Public Library's NYPL Digital Gallery has access to over 600,000 images
PRIMARY SOURCES: DOCUMENTS
Avalon Project from Yale University - click on century of interest
Chicago Historical Society -- for primary sources on local events -- Look at other state or local historical societies for more information
Digital History from the University of Houston: Scroll down to find the time period for your project or on the LEFT click on primary sources (especially Landmark documents); see additional modules on American history
History Matters from George Mason University has links to primary documents and photographs related to US history.
Internet Modern History Sourcebook from Fordham University -- choose a time period relevant to your topic
National Archives and Records Administration for links to 100 milestone documents in American history.
National History Day (sponsored by University of Maryland and others) list of online primary sources
Presidential Speeches (last updated 2007)- by sliding the bar, go to the time period of interest; this tag cloud shows by word size and brightness intensity key issues of the day.
State Historical Societies may also have images and suggested links
United States Historical Documents - a Chronology from University of Oklahoma
PRIMARY SOURCES: STATISTICS
Historical Census Statistics - interactive site for calculations hosted at the University of Virginia.