The CIA World Factbook 2013 by 
The World Almanac World Fact Book by 
The Statesman's Yearbook 2007 by
Human Development Reports and Indicators Produced by the United Nations Human Development Programme.
International Database (IDB) From the U.S. Census Bureau, provides tables, country rankings, and world population information.
International Statistical Agencies Links to international statistical agencies.
NationMaster.com Statistics worldwide on the environment, education, energy, immigration, terrorism, transportation, and more.
Statistical Abstract of the United States Examine Section 30, which gives comparative international statistics.
United Nations Development Programme/Human Development Reports Rates countries by Human Development Index, which entails life expectancy, literacy and school enrollment, and standard of living.
United Nations Infonation Enables a comparison of statistical information on United Nations member states in the fields of population, economy, health, technology, and the environment.
United Nations Statistics Division. UNdata. Search page that allows users to search and download a variety of statistics from the United Nations
World Bank: Data by Country Organized by income level and geographic region or specific country; includes data on population, environment, and the economy.