The World Factbook

The World Factbook provides national-level information on countries, territories, and dependencies. It is an authoritative source. The information includes a summary of each entity’s people, history, economy, geography, communications, transportation, and more. It is updated every few weeks.

This reference provides basic and up-to-date information, including a map, lots of basic geography, resources, and population facts, government, military and transnational issues.  There is also a link that displays a gallery of country flags.