The Library of Congress Digital Collection is a wonderful resource for primary sources. Note the field on the left of the webpage. You can search by
If you use the dropdown menu at the top, you can switch from Digital Collection to Personal Narrative. In Personal Narrative, you will find interviews with people, and in particular a large selection of interviews with veterans.
Likewise, you can view the collection of Political Cartoons from the eighteenth and nineteenth centuries.
The United States Holocaust Memorial Museum has over 200,000 artifacts, films, photos, and more which are searchable through this website. It also includes the Holocaust Encyclopedia which provides background information on the Holocaust.
The Smithsonian Institution is more than cool museums! It is a repository of millions of cultural artifacts, art works, and documents. The search interface can be a little clunky, but it is worth it.
ProQuest's Historical Newspaper database has full coverage of 36 newspapers going back into the 1700s, most articles are from the 20th century, however. Newspapers include The Washington Post, The New York Times, The Wall Street Journal, and other well known publications. Depending on your topic, you might prefer a regional newspaper, such as The Atlanta Journal or The Chicago Tribune.
Photo by beanworks at Morguefile.com, used under creative commons license.
The Black Life in America database searches more than 19,000 American and global news sources, including over 400 current and historical Black publications. This database covers from the 1700s to the present and is a rich source of information!
"Founded in 1985 by journalists and scholars to check rising government secrecy, the National Security Archive combines a unique range of functions: investigative journalism center, research institute on international affairs, library and archive of declassified U.S. documents ("the world's largest nongovernmental collection" according to the Los Angeles Times), leading non-profit user of the U.S. Freedom of Information Act, public interest law firm defending and expanding public access to government information, global advocate of open government, and indexer and publisher of former secrets."
The National Archives have a rich set of data, but it might take a little more digging to find. You can search in a search bar, but also within collections such as War and Military Records, Founding Documents, specific places or subpopulations such as Women.
The Office of the Historian of the State Department contains documents related to Foreign policy going back to the Lincoln Administration. Documents are organized by Presidential term, year within term, and topic within year. Background knowledge is very helpful in searching this site.
The Primary Source Sets of the Digital Public Library of America (DPLA) are curated around specific topics. Each set contains numerous primary sources including images, music, interviews and more. There are many, so you will need to scroll through to see if your topic is included.
Houghton Library at Harvard University has made a large collection of primary source materials pertaining to Black Experiences with Slavery, Abolition, Emancipation, and Freedom available in digital format. It is a wide-ranging collection of materials from 1780-1920.