GeoIP

MaxMind GeoIP is a collection of APIs for looking up the location of an IP address. It includes support for lookup of country, region, city, latitude, and longitude. Free GeoLite databases are available for the country and city.

Reference

GeoIP: http://www.maxmind.com/app/ip-location
GeoIP for your IP address: http://www.maxmind.com/app/locate_my_ip
GeoIP Python API: http://www.maxmind.com/app/python
pygeoip: http://code.google.com/p/pygeoip/