UN site providing data on the world, as well as on specific countries. Check out the "data" and "publications" sections -- there's also information about urbanization (and gender and other interesting issues, too).
The World Factbook, produced for US policymakers and coordinated throughout the US Intelligence Community, marshals facts on every country, dependency, and geographic entity in the world. We share this information with the people of all nations in the belief that knowledge of the truth underpins the functioning of free societies.