This year has certainly been the time for governments opening data. It's also ripe with public mashup contests, from big U.S. cities to large-scale propositions from down under. Here's an overview of some of the recently-launched government data contests.
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.