There are a lot of great digital collections online. Browse some of those listed below, and please let us know if you have others that you would like to see listed here via Ask a Librarian
The American Presidency Project: Site contains documents related to the study of the American Presidency, including public papers, annual messages to Congress, inaugural addresses, radio addresses, state of the union addresses, acceptance speeches, presidential candidates debates, party platforms, elections data, and an audio/video archive.
Calisphere - the University of California's free gateway to a world of primary sources, including photographs, documents, newspaper pages, political cartoons, works of art, diaries, transcribed oral histories, advertising, and other unique cultural artifacts. Browse by California time period or topic, institutional collections, or using an A-Z listing.
Connecticut Digital Archive - The CTDA is part of the Digital Preservation Repository Program at the University of Connecticut. We serve the entire state and are dedicated to the maintenance, delivery, and preservation of a wide range of digital resources for educational and cultural institutions and State Agencies in Connecticut.
Cornell University Digital Collections: the Cornell University Library Digital Collections portal aggregates rich digital collections into a single website, with the goal of enabling easier access and discovery of content.
Documenting the American South (DocSouth): A digital publishing initiative from the University of North Carolina at Chapel Hill that provides Internet access to texts, images, and audio files related to southern history, literature, and culture. Currently DocSouth includes sixteen thematic collections of books, diaries, posters, artifacts, letters, oral history interviews, and songs.
The Digital Public Library of America is a portal to digital resources from archives, libraries, and museums around the country that provides access to millions of items that can be searched by timeline, map, format, or topic. It is super easy to browse chronologically, for example, and identify items and collections that are incredibly useful.
The Digital Collections of Harvard College Library: Wide ranging and extensive collections of many sorts, including audio poetry recordings, The Emily Dickinson Archive, Papyri, Early Photography of Japan, Photographs of the New England Landscape, Russian Theater Designs, Map Collections, Manuscript collections.
The Internet Archive collects and shares millions of free books, films, software, audio recordings, websites, and more!
Library of Congress Digitl Collections: The digital archive of the Library of Congress, the largest library in the world, containing millions of books, manuscripts, photographs, newspapers, maps, and recordings.
The MET's Heilbrunn Timeline of Art History - browse the Met’s collection via a chronological, geographical, and thematic exploration of global art history to gain access to and information about thousands of art objects that may be considered as primary sources.
The National Archives and Records Administration (NARA): The nation's record keeper. Of all documents and materials created in the course of business conducted by the United States Federal government, only 1%-3% are so important for legal or historical reasons that they are kept in the Archives forever.
New York Public Library Digital Collections - search through hundreds of thousands of digital items from this world renown collection. After submitting a search use the browse options on the left to narrow down.
Smithsonian Collections: An immense colection of national and international heritage, Browse by topic or search through millions of objects spanning over a billion years of history.
University of Michigan's Digital Collections: Includes 251 digital collections that can be easily browsed or searched. Try browsing the collections by using the subject filters on the left-hand side of the screen.
Yale University Library Digital Collections: This site provides access to millions of digitized works and images. New materials are added regularly. There are Yale Library collections that are not available on this site. More information on additional collections can be found here.