The Google Places iOS library by Lukas Kukacka uses a simple block interface to interact with the features of the API that include mapping, localization, and reference. This project offers place search, with nearby search and text search. It also provides places details, with a more detailed information about a specific location. Available as CocoaPods.
Take a look at MapCruncher. A very interesting new map mashup technique from the folks at Microsoft Research. It basically allows you to overlay any digital map image on top of a normal, zoomable Virtual Earth map.
Normally we'd give a brand new site a break for not immediately having an API. When it comes to the rabidly popular FourSquare, which launched in March, developers have been clamoring to build on top of the service. So, today's launch of the FourSquare API (our FourSquare API profile) is bound to be met with extreme enthusiasm.
Wikimapia is a web service that allows users to edit information on a world map in a wiki format. Users of the site can add places, edit them, and get the information previous users have entered. The info there is currently pretty sparse, but the service is rather new. The company also recently released a Wikimapia API that supports getting information from the web service.