Google's geocoding api does what want you want. As Xerus points out, as long as you are not using the geocoded points on a non-google Map, you should be good (terms of service). Specifically,
3.1 Use without a Google Map. Customer may use Google Maps Content from the Geocoding API in Customer Applications without a corresponding Google Map.
3.3 No use with a non-Google map. Customer must not use Google Maps Content from the Geocoding API in conjunction with a non-Google map.