The WordPress IP to Country Plugin converts an IP address to a country and provides the country code. For example, you could (no, I haven't implemented this here, so test comments won't help) display the commenter's country based on their IP address (though this would obviously be misleading for Tor users). Also interesting is the reference to the IP-To-Country Database, which appears to be freely available. Useful for your own projects, such as analyzing log file statistics.