World Flag Database
This site offers more than 260 pages of country flag images plus a special section on flags from WWII and the Vietnam War.
Flag Facts on GovSpot.com
Lengthy list of resources on flags. Includes everything from state flags and flag-related news to a how-to site on finding out a flag's country of origin if you only know its design.
Once you've become an expert, test how well you know your flags with this game designed by the United Nations.