"GeoNames is a free and open source geographical database. Primarily for developers wanting to integrate the project into web services and applications, it integrates world-wide geographical data including names of places in various languages, elevation, population, and all latitude / longitude coordinates. Users are able to manually edit, correct and add new names with a user-friendly wiki interface. The data is accessible through a number of webservices and a daily database export.
"Launched at the end of 2005, GeoNames is already serving up to over 3 million web service requests per day, and contains over eight million geographical names..."