ZipCarton is a plugin for your Mac OS X Address Book that tries to find the ZIP or postal code for the city you entered in your contact's details.
ZipCarton is completly free, open source and can find postcodes in 45 countries: Andorra, Australia, Austria, Bangladesh, Belgium, Bulgaria, Brazil, Canada, Croatia, Czech Republic, Denmark, Faroe Islands, Finland, France, Germany, Greenland, Hungary, Iceland, India, Italy, Japan, Liechtenstein, Luxembourg, Macedonia, Mexico, Moldova, Monaco, Netherlands, New Zealand, Norway, Pakistan, Poland, Portugal, San Marino, Slovakia, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Thailand, United Kingdom, United States and the Vatican (using Geonames).
ZipCarton will only replace the postal code if it finds a single match in the GeoNames postal code database. It will ask to open the GeoNames website when multiple possibilities are found.
ZipCarton is localized in Danish, Dutch, English, French, German, Italian, Japanese, Portuguese and Spanish.