http://webpmt.usps.gov/pmt008.cfm
USPS list of post offices by zip code. Not ment as a zipcode to city state
database, but in most cases... Note that the missing zip codes are typically
the same city/state as the ones before, e.g. 92025 is Escondido, CA and 92026
and 7 are not listed: They are also Escondido, CA.