Using data from the Audioscrobbler API and Amazon, tuneglue can visualize webs of relationships around any artist in Last.fm’s data catalog.
GeoPlanet Explorer, a tool for browsing the Yahoo! geolocation hierarchical database, GeoPlanet.
The tool queries Yahoo’s GeoPlanet API for a WOEID of a “place,” which is Yahoo’s clever method of uniquely identifying any “location of interest” in the world, with something more loose yet more descriptive than just a lat/long. Passing a WOEID to the API returns lists of locations spatially-related to your search, like parent/child/sibling places and historical “ancestor” records.
The developer used YQL, YUI, and Yahoo Maps to put it all together. Check out the source code on Github for the full experience.