This is an update to a previous post where I lamented on Google’s lack of a geocoding feature in their Google Maps API. I suggested that you combine Yahoo’s Geocoding API with Google’s to get the functionality that you might need.
They just added a Geocoding feature to their API, though! Here’s an article that goes more into it:
http://ajaxian.com/archives/geocoding-with-googles-maps-api
Here’s the Official Google Maps API Blog Post:
http://googlemapsapi.blogspot.com/2006/06/geocoding-at-last.html