UNdata is an Internet search engine that retrieves data from statistical databases provided by the United Nations.
American Fact Finder (U.S. Census Bureau)
DataCite (search engine)
DataVerse (Harvard)
World's largest collection of social science research data.
FedStats
Search for statistics from 70+ Federal statistical agencies.
Google Data Set Search
Search engine dedicated to finding data repositories on the web.
Pew Research Center
Access free data and reports documenting the impact of technology on American life.
Statistical Abstracts 1870s-2010s (U.S. Census Bureau)
Biographical Dictionary
Contains brief biographical information on "28,000 notable men and women who have shaped our world from ancient times to the present day. The dictionary can be searched by birth years, death years, positions held, professions, literary and artistic works, achievements, and other keywords."
Biographical Directory of the U.S. Congress: 1774 to Present
GUIDE: Biographical Perspectives
Federal Agencies and Branches of the Government
AnyWho (AT&T)
Geographic Name Directory (Getty Research Institute)
Britannica Encyclopedia | Mobile | Español | Atlas (via Badgerlink)
Funk & Wagnall's New World Encyclopedia (via Badgerlink)
GUIDE: What about Wikipedia?
No Sweat Tech: Finding Old Instruction Manuals for Free Online (The Saturday Evening Post, August 19, 2019)
Google Maps | Google Earth | Google Street View
Also:
Open Street Map
A map of the world, created by users and free to use under open license.
Historical Maps
Identify the Source of a Quotation