Google Maps

Google Maps is a Web, mobile app, and developer API service which displays maps of the Earth from global to local levels. It is "free" in the sense of not costing anything for consumer uses, but not in the sense of being actually open and free of proprietary content; that's why Open Street Map was created as a noncommercial competitor.

Developer API info

 * Google Maps Developer Documentation

Third-party API additions

 * Mapnificent: add transit time info to Google maps
 * gmaps.js: Simplified Google Maps API

Other links

 * Official site
 * Wikipedia article