Free Digital Libraries
The largest open-access (free) digital libraries are Google Books, the Hathi Trust Digital Library, and Europeana. Other major projects include the Library of Congress American Memory Project, Making of America (19th-century U.S. History), and the New York Public Library Digital Collections.
Hundreds of smaller, regional digital libraries exist. For lists of the most significant resources, see:
A great free resource for historical maps is the David Rumsey Map Collection.
Newspapers and news broadcasts are excellent ways of experiencing and understanding history as it happened.
For an overview of available resources, see this database list: