United States Facts and Statistics 

• American FactFinder
  Information from the U.S. Census Bureau.
• Bureau of Justice - Statistics
  Crime, law enforcement, and courts statistics from the U.S. Department of Justice
• Bureau of Transportation Statistics
  All sorts of information and statistics about transportation in the U.S., by car, train, plane, boat, and other means.
• Crime in the United States
  "The Uniform Crime Reporting (UCR) Program is a nationwide, cooperative statistical effort of more than 17,000 city, university and college, county, state, tribal, and federal law enforcement agencies voluntarily reporting data on crimes brought to their attention."
• Federal Agency Statistics Reports
  From the U.S. Census Bureau.
• FedStats.gov
  "The gateway to statistics from over 100 U.S. Federal agencies".
• Historical Census Browser
  "The data presented here describe the population and economy of U.S. states and counties from 1790 to 1960."
• On This Day
  From the New York Times, a list of historical events, famous birthdays, and a free copy of a selected NY Times article dealing with a featured historical story.
• Social Explorer Maps
  Information from the U.S. Census and other sources displayed as interactive maps.
• Statistical Abstract of the United States
  "The Statistical Abstract of the United States, published since 1878, is the authoritative and comprehensive summary of statistics on the social, political, and economic organization of the United States." Adobe downloads here.
• Today in History
  From the Library of Congress.
• U.S. Census Bureau
  People, business, geography... all sorts of facts and figures from the U.S. Census Bureau. Check out the US Census Atlas, CensusScope, and the Publications page "featuring data reports for historical Censuses and for Statistical Abstracts".

 World and General Statistics 

• Earth: A Graphic Look at the State of the World
  Via maps and graphs, this site shows and compares information on such topics as global ecology, human conditions, energy supply, food production, pollution, warfare, and wealth.
• Free Economic, Demographic & Financial Data
  "Our databases contain more than 165 million economic, financial, and demographic time series covering more than 180 countries and their sub-regions. Accuracy and timeliness are two of the hallmarks of Moody's Economy.com economic databases."
• GEO-3 Data Compendium
  "The web site includes data tables for environmental issues as addressed by UNEP's GEO, such as climate change, water stress and deforestation, as well as a wide variety of socio-economic variables."
• GeoHive: Global Statistics
  "A site with geopolitical data, statistics on the human population, Earth and more. The main kind of data you can find here is population statistics of regions, countries, provinces and cities."
• OFFSTATS
  Official statistics on the web; find by country, region, or topic.
• The UC Atlas of Global Inequality
  "The Atlas of Global Inequality explores some aspects of inequality using online, downloadable maps and graphics. All these materials can be used freely providing they are attributed to the UC Atlas of Global Inequality."
• World Stats Clock
  Estimates of current world statistics, including population, births, deaths, incidence of various diseases, global temperature, and other information.
• ZipSkinny
  "Enter your ZIP Code to see U.S. Census data and comparisons with neighboring ZIPs."