Guesses your visitor’s Country from his IP. You can then add commenter’s nation flags next to their name in comments, for example.
For documentation and tips, please refer to the official plugin page for <a href="http://planetozh.com/blog/archives/2004/08/27/ip-to-nation-plugin/" title="IP to Nation" rel="nofollow ugc">IP to Nation</a>

Ozh's IP To Nation

Guesses your visitor's Country from his IP

Dave Ligthart

Get country by ip. Installs the ip2nation database.
Use this plugins functions to get the country / country code 
by ip address from your template file.
See <a href="http://www.ip2nation.com/" rel="nofollow ugc">ip2nation.com</a>.

WP-IP2Nation-Installer

Get country by ip. Installs the ip2nation database.

Ozh's IP To Nation vs WP-IP2Nation-Installer