There are presently two versions fo the file. One with multiple city/town names that the Postal Service recognizes as associated with each zip code. That is, a zip code may appear multiple times with different city names. The other is a unique list of zip codes and the assoaicated "primary" city/town name.
All Locations file (8.7 MB, last updated 1/22/2012)
Unique Zip code file (4.2 MB, last updated 1/22/2012)