The World Gazetteer provides a comprehensive set of population data and related statistics

Population data arranged by country

Current population figures and area size for all countries and important territories
Population figures and area size of administrative divisions
Population figures for the largest cities, towns and places as well as for metropolitan areas
Historical population data (census or estimates; mostly from last or last two censuses)
Overview maps that show the position of the country or the administrative divisions

Related data

Summary statistics for countries and territories as well as for the largest cities and agglomerations
Current national flags
Summary maps for various subject
A pronunciation guide for some languages
There is a downloadable file for offline research
A population clock that show the current population of the world
Comprehensive meta informationen about statistics and the project