MapQ is an easy to use wrapper for the Mapquest Geocoding API. It advises developers to interact with the API by making the environment variable in the local environment. Developers can also interact with the Geo class to work with the API.
Two days ago we wrote about Urban Airship grounding SimpleGeo APIs. While one API was being taken over by another company, it left SimpleGeo's innovative flagship geo storage product stranded. Another company has quickly come forward to pick up the slack. Geoloqi created a SimpleGeo importer that will move storage from one platform to the other, where places can then be queried by the Geoloqi API.
Gowalla, Foursquare, Yelp, Facebook Places, the list goes on. There's certainly no shortage of methods to tell people where you are and what you're doing while you're there. Startup Whatser, built on the SoGeo API for location-based apps, has jumped into the ring with a different approach to check-in services: to be useful.