USPS address normalization:
http://www.qualifiedaddress.com/They are CASS Certified and charge $0.26 per address. They have APIs that allow for the address standardization. Write some quick data cleanup tools and then a jQuery script to run this along with the shopping cart. The main issue being cost of course so i'd recommend using Google Geocoding for the initial user interaction then use them after the order is about to be submitted just to verify the address one more time.
This probably should be posted somewhere else.
