http://ws.geonames.org/findNearbyPostalCodes?lat=40.775676&lng=-73.984484

http://ws.geonames.org/findNearbyPostalCodes?lat=40.775676&lng=-73.984484

This will return an XML that looks like this.

<code>
<postalcode>10079</postalcode>
<name>New York City</name>
<countryCode>US</countryCode>
<lat>40.780751</lat>
<lng>-73.977182</lng>
<adminCode1>NY</adminCode1>
<adminName1>New York</adminName1>
<adminCode2>061</adminCode2>
<adminName2>New York</adminName2>
<adminCode3/>
<adminName3/>
<distance>0.8345131270291027</distance>
</code>

Web link to convert long/lat city, state, etc...

Objective C