Locating people internationally?

Right now I'm trying to make a project of mine more internationally friendly. As of now I rely on zip codes for my service. Is there a good method for determining locals other than postal codes? Or does anyone know of any up-to-date databases of international postal codes other than U.S. codes?

What I'm thinking would be cool is if users could click on a google map, so google could then identify their latitude and longitude and hand us off their postal code, city, etc through an api of some sort. This link is all I could find with my time: http://conversationswithmyself.com/googleMapDemo.html