Wikimapia is a web service that allows users to edit information on a world map in a wiki format. Users of the site can add places, edit them, and get the information previous users have entered. The info there is currently pretty sparse, but the service is rather new. The company also recently released a Wikimapia API that supports getting information from the web service.
A community-minded API has a politcal message for the UK's Royal Mail: open up the postal code database. ErnestMarples.com is named after the former postmaster general who apparently first oversaw the introduction of the postal code in the UK.
For several years millions have shared the places they've been using the Where I've Been website and Facebook application. The site also has an API (our Where I've Been API profile), which allows for much of the same functionality, such as searching countries, marking it visited and adding content such as a story or photo.