So, I was using one of Google’s sign up forms, and I noticed that it gave me a nice tip – The valid zip codes for my state! Along with some sample zip codes for my country (usa). I opened up the firebug console and checked out the ajax call – it was this:
That’s really cool. It returned an XML document with all the state’s valid zipcodes. While it may be unreliable to make this same AJAX call from within your own web application every time, the XML document itself is quite valuable with the zip code validation.
Download that XML document here.