A free geocoding service
Geocoder.us provides a free XMLRPC gateway to the TIGER data. It does not appear to do any sort of reverse geocoding, however. Here is how you can easily use it in Python…
>>> import xmlrpclib
>>> p = xmlrpclib.ServerProxy('http://rpc.geocoder.us/service/xmlrpc')
>>> p.geocode('110 North Russell, Ames, Iowa')
[{'city': 'Ames', 'prefix': 'N', 'suffix': '', 'zip': 50010,
'number': 110, 'long': -93.628218000000004, 'state': 'IA', 'street':
'Russell', 'lat': 42.022807999999998, 'type': 'Ave'}]
>>>