Newspapers.com World Collection is an extensive database that provides online access to 4,000+ historical newspapers. Dating from the early 1700s into the 2000s, Newspapers.com Library Edition contains full runs and portions of runs of well-known, regional, and state titles to small local newspapers in the United States and other countries.
Indigenous Newspapers in North America aims to present a diverse and robust collection of print journalism from Indigenous peoples of the US and Canada over more than 9,000 individual editions from 1828-2016. 
The United States Holocaust Memorial Museum Encyclopedia of Camps and Ghettos, 1933-1945 provides authoritative documentation of camps, ghettos, and other persecutory sites operated by the Nazi regime and its allies in a vast network that extended across the European continent and reached as far as the Soviet Union and North Africa. It is the most comprehensive resource on the Nazi camp universe, detailing the complexities of the camps and their impact on millions of inmates.
A discontinued project by Google to scan and index historic newspapers. The Google News Archive is still available and a great resource that makes many difficult to find newspapers available freely online. 
Historic U.S. Free Online Protestant Newspapers is a list of free online historic Protestant newspapers from across the Unites States. The list is broken down by state and dates range from the early 1800s to today. 
This online collection presents newspapers edited by Frederick Douglass (1818-1895), the African American abolitionist who escaped slavery and became one of the most famous orators, authors, and journalists of the 19th century. 
The Public Domain Image Archive (PDIA) is a curated collection of more than 10,000 out-of-copyright historical images, free for all to explore and reuse. 
The Theological Commons is a digital library of over 150,000 resources on theology and religion. Developed in partnership with the Internet Archive, it contains books, journals, audio recordings, photographs, manuscripts, and other formats dating from 975 C.E. to the present. 
The processed records of the NAACP Legal Defense and Educational Fund consist of approximately 80,000 items of which more than 90% (251,413 images) have been digitized and open for research use. 
The LGBTQ+ Studies Web Archive collects and preserves online content which documents LGBTQ+ history, scholarship, and culture in the United States and around the world. 