This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
You can license current ZIP data from the USPS and integrate it into your app directly; that's probably the fastest approach. The USPS may also have a web API. From past experience I would guess that neither option is free.