Today at Where 2.0 Yahoo announced the release of Placemaker, a new "geo-enrichment" platform. The freely-available platform, which includes an API (our Placemaker API Profile), enables developers and publishers to make applications and data sets location-aware by determining the "whereness" of unstructured content (such as blog posts, new articles, feeds, and web pages).
Quick, what is your House of Representatives district? Many people don't know this number, or the member who represents them. The New York Times' new Districts API makes it easy for your application to answer the question for any point within New York City, though it could serve as a template for a nationwide--or even international--service.