In the process of downloading the alpha release of MySQL Administrator (which looks quite solid and useful) I noticed on the download page (for Win binaries) a reference to MaxMind GeoIP.
MaxMind offers a product to Obtain the Country, Region, City, Latitude, and Longitude of any IP address., the GeoIP City Edition claims to drill down to World Region Code, City Name, Postal Code, Latitude nad Longitude, DMA Code (Designated Market Area, US only), and Area Code.
It might be worth a look. The only other alternates I’m aware of are CountryHawk and GeoBytes.
MaMind also provides some standard list such as :
ISO 3166 Country Codes,
Region Codes: For US/Canada, ISO-3166-2 code for the state/province name. Outside of the US and Canada, FIPS 10-4 codes.
Designated Market Area (DMA) codes (US only) contains metro regions in the US based on TV demographics. Designated Market Area (DMA) is a Nielsen Media Research term better defined here.