A three-part standard - ISO 3166
describes the respective functions of the standard's three parts.
Internet Country Codes
An alphabetic list of the two-letter letter country codes used as internet top level domains, with the English-language country names.
ISO 3166
Code lists and updates, from the official ISO site.
ISO 3166 Maintenance Agency (ISO 3166/MA)
Page of the organization which maintains the ISO 3166 list of country codes. Downloadable list of the two letter country codes and French or English country names.
USPS ICL to ISO 3166 Mapping
Mapping of United States Postal Service Index of Countries and Localities to ISO 3166 codes.