CoorZip (made by: Kevin Ko aka uhelios)
http://uhelios.com

UPDATE 2:
- Saves Result in a Text File
- More efficient

UPDATE 3:
- Enables individual coordinate conversion
- Added Icon

UPDATE 4:
- Made cool-down faster
- Minor bug fixed

UPDATE 5:
- Compatible with 10.6+
- Fixed memory leak (now much faster)

UPDATE 6:
- Added XML (uses yahoo's)

UPDATE 7: 
- Parsing error in CSV fixed

UPDATE 8:
- Added option to stop the conversoin (XML only)
- Garbage Collection enabled (XML only)
- Increased Speed (XML only)

CoorZip is a utility that imports CSV (Excel documents) that contain latitude/longitude coordinates or individual
coordinates and converts them to U.S. Postal Zipcodes through Google's & Yahoo's Reverse Geocoding API by JSON or XML parsing.

Example of a CSV document that can be used:

48.85,-92.55
48.85,-92.45
48.75,-123.65
48.75,-123.55
48.75,-123.45
48.75,-123.35
48.75,-123.25
48.75,-123.15
48.75,-123.05
48.75,-122.95

CSV documents are basically text files that contain a comma as a separator between each column.
Thus, you can just make a simple text file and rename the extension to .csv to fit your needs.
*Note: This utility only reads CSV documents as floats, NOT STRINGS/TEXT! So get rid of the quotation marks!*

As CoorZip imports the data, you are able to execute these coordinates to be converted into zipcodes based
on Google's Reverse Geocoding API found here: http://code.google.com/apis/maps/documentation/geocoding/
and Yahoo's PlaceFinder API found here: http://developer.yahoo.com/geo/placefinder/

The format for the URL, as shown in the documentation, is as so:

(google) http://maps.googleapis.com/maps/api/geocode/json?latlng={latitude},{longitude}&sensor=true

Replacing {latitude} & {longitude} with the appropriate coordinate values.
By loading this URL through CoorZip and finding the return value, it provides us with all the necessary
information to find the postal zip code.

The return value is in JSON or XML format, which is preferred because of its quick and easy
parsing methods. To parse the JSON, CoorZip uses the yajl-objc framework. 

A NSArray is formed by taking the raw JSON and using [json YAJL_JSON];
Where json is the return value from the Google API.

For XML, we simply ignore everything except between the <postal></postal> tags. This is only for
Yahoo's API.

From this we can easily search the NSArray and the sub-arrays for the postal_code.
We loop this until the CSV document has reached its end and leaving 4/10 of a second to "cool off" and
prevent a memory-overload (for cases if you have over 1,000 pairs in the CSV document).

*Note: Google's Reverse Geocoding only allows 2,500 queries per day!!*
*Note: Yahoo's PlaceFinder allows 50,000 queries per day!!*

Finally, we make it so that it saves the result into a text file on the desktop named coorzip.txt.