The Smithsonian Institute offers a wide variety of primary resources that deal with many topics, including political, military and technological history. There is a special section for researchers, where users can browse through the collections to find a multitude of primary resources, such as canceled stamps from early America and art collections from different times in history.
The Library of Congress is an excellent database of various collections that researchers can access for firsthand information. For example, in the American History section, researchers can find topics as varied as the last 50 years of Coca-Cola advertising, firsthand accounts of former slaves and a magazine advertisement featuring Harry Houdini. The site takes some getting used to when first navigating, but the information found should be worthwhile to eager researchers.
Those interested in finding ancient history resources might want to visit the Perseus Digital Library, which is an online collection of both primary and secondary sources. The database collection is vast and contains texts and images that researchers can utilize for their projects. One highlight of interest is their artifact browser, which allows researchers to view photos of archeological artifacts, such as vases, coins, buildings and sculptures.
The University of Oklahoma College of Law offers an extensive collection of documents in U.S. History. The various documents include a pre-Colonial letter from Christopher Columbus to the King and Queen of Spain, all the way to current President Barack Obama's Inaugural Address.