C# Reusable code/library for postal/zip code lookup

Does anyone know of a good piece of code that can deal with Zip 开发者_运维知识库code lookups where a user enters a zip code to look for a service provider in an area, and if none are found you can expand the search to all zip/postal codes within X radius of the original zip/postal code?

There are a variety of web services out that that you may reference from c#. I suggest you enter "free zip code lookup webservice" into your favorite search engine. One example is: http://www.zipcodedepot.com/free_zipcode_soap.html