I know that the google geocoding api has a 2,500 hits a day limit before it\'ll start returning REQUEST_DENIED. How many does the bing one take? I heard that it\'s unlimited
By the way you can also try Yandex Geocoding API which is for free for up to 25.000 Requests per day per Website/Mobile App:
http://api.yandex.com/maps/doc/geocoder/desc/concepts/input_params.xml