International Air Transport Association airport code – Wiki page on the history and conventions of the three-letter code designating airports around the world, as defined by the International Air Transport Association (IATA).
World Airport Codes – Information for almost every airport in the world. Search for airport codes by country, city, airport name, or airport code.
Airport City Codes – Database listing nearly 9,000 airports used by commercial airlines.
Airport Codes – A complete list of US and international Airport Codes.