Demographic

International Data Base (Census Bureau) - - time series data for a variety of demographic indicators for countries and areas of the world with a population of 5,000 or more

City Populations - major cities and agglomerations around the world, also has maps

United Nations

• UN Statistics Division - Demographic Yearbook and other databases, currency varies for countries, some areas require a subscription
• United Nations Data - - data areas fo countries and topics: gender, health, human development, trade, tourism, information communications technology, energy, education, and crime.
• FAOSTAT  (United Nations) - Food and Agriculture Organization

World Factbook (CIA) 

World Bank

• Doing Business (World Bank) -  compare business regulations, data and reports
• Global Poverty and Equity Indicators Portal - front page with charts and link to databank  (World Bank)

OECD Statistics (Organisation for Economic Co-operation and Development) - frequently-requested variables