Read all the way to the end - there's a bonus!
nowCOAST LayerInfo API: nowCOAST is a GIS-based online mapping tool that provides access to real-time coastal environmental observations and NOAA forecasts for any region in the coastal United States. nowCOAST's LayerInfo API provides access to additional useful information on mapping layers, including Legends, Timestamps, Icons, and Layer Descriptions. The API uses HTTP calls and responses are formatted in XML, HTML and TXT.
Aviresto API: Aviresto is a guide to restaurants in France. The site lets users read and submit customer reviews. Searches can be conducted by city or by location on a map. An API is available that allows users to conduct these searches programmatically and pull the results into their own application or web site. Public documentation of the API is not available; developers should contact the provider for access.
NAVTEQ LocationPoint Advertising API: NAVTEQ is a provider for digital maps and map content used in navigation and location-based services. The NAVTEQ Network for Developers (NN4D) program provides developers with a variety of API's for mapping, road traffic data, and advertising.
The NAVTEQ LocationPoint Advertising (LPA) service is an in-application mobile advertising service that provides location-based, targeted advertising to users of location aware applications and mobile websites. This API will gather location data and identify users, and then request relevant adds to return to the device. The LPA web service also exposes functions for handling the end-user experience after they have interacted with a LPA-powered add; for example, providing the user with maps and routes to physical stores related to an add they clicked through.
NAVTEQ Map Reporter API: NAVTEQ is a provider for digital maps and map content used in navigation and location-based services. The NAVTEQ Network for Developers (NN4D) program provides developers with a variety of API's for mapping, road traffic data, and advertising.
NAVTEQ's Map Reporter allows individuals to suggest updates or corrections to NAVTEQ maps. Users can give feedback about addresses, roads or road features, points of interest, or traffic restrictions. Attachments, such as images or supporting evidence, can also be added to the submission. In addition to submitting feedback on existing map elements, users can suggest new map content such as other points of interest or cartography details. The Map Reporter web service is composed of two primary parts: a submission service that allows users to provide their feedback to NAVTEQ, and a query service for searching map reports for the status and details of previously submitted requests.
Bonus: StreetFight offers Comparing the Pros and Cons of 5 Top Location APIs which looks at contenders to fill in for recently closed SimpleGeo. Warning: written by an intern.