Geo::IP::PurePerl uses a file based database. This database simply contains 
IP blocks as keys, and countries as values. This database is more complete 
and accurate than reverse DNS lookups.

Geo::IP::PurePerl can be used to automatically select the geographically 
closest mirror, to analyze your web server logs to determine the countries 
of your visiters, for credit card fraud detection, and for software export 
controls.

WWW: http://search.cpan.org/dist/Geo-IP-PurePerl/