In case it's not known by everybody, you can geocode(maybe also reverse geocode, I didn't check) US addresses in batch with TIGER census data and PostGIS.
It's not directly relate to topic (dynamic maps, online geocoding), but somewhat relevant.
With about $300 in Amazon EC2 I geocoded 18 million addresses in 3 months. You probably can do it with your own PC with similar time (the only hardware requirement is RAM and SSD).