Availible in WSN Classifieds since the beginning, and in Links, Gallery and KB from 4.2.0, the zip code range search offers a way for visitors to find items near their zip code.

The available database only covers the USA, so this switch is only useful for Americans or for people who have a database they know how to adapt and insert. WSN will attempt to load the data at the time you turn the switch on, but may encounter out of memory or timeout errors due to the huge size of the database. If you get errors, you'll need to follow a manual procedure:
1) Save zipdata.sql to your computer (right-click, save target as).
2) Open zipdata.sql in a text editor. Use the editor's search and replace functionality to replace every instance of {PREFIX} with the tables prefix you use -- if you didn't change the default during setup then it's wsnlinks_. Save the changes and exit.
3) Open PHPMyAdmin, navigate to the database WSN Links is installed in, click the sql tab, and supply the zipdata.sql file for upload there.

Once activated, the front page simple search and advanced search page will contain options to search within x miles of a zip code. You can copy the HTML out of those templates if you want to place it elsewhere.