Maps has support for several geocoding services. Some of them have restricted licences, others are completely open source. You can take out geocoding services you don't need by removing them from the $egMapsAvailableGeoServices setting.
The 'Geoservice param value' is the value you need to pass along with any geoservice parameter.
|Geocoding service||Geoservice param value||Description||Licence||Max requests||Last change in version|
|GeoNames||geonames||Free geocoding service with over 8 million objects||Creative Commons attribution||unknown||0.3|
|Google (geocoding)||Geocoding service provided by Google that can only be used for displaying Google Maps maps||A Google licence||50,000 per day||0.1|
|Yahoo! (geocoding)||yahoo||Geocoding service provided by Yahoo!||A Yahoo! licence||50,000 per day||0.1|