Foursquare has embraced the open maps movement. Russia's biggest search engine integrates with the Topsy API. Plus: Disqus comments available in Gnip, Microsoft launches its own Webmaster Tools API and 21 new APIs.
There are any number of questions that can be answered by Wikipedia, but you can add "where am I?" to the list. Given any latitude/longitude coordinates, the WikiLocation API will find you corresponding Wikipedia articles to tell you about your surroundings.
Google has just announced a nice addition to the Google Gears Geolocation API: the ability to use WiFi on laptops to locate users to within 200m accuracy in major desktop browsers in hundreds of cities around the world. We originally covered the GeoLocation API back in August, when Google first announced the release of the API for use in mobile devices to get a more precise estimate of a user's location.