Freegeoip

Once installed and auto-enabled, the plugin will request IP address based geolocation information from your site's visitors and add that information to their Joomla user session. Access that information as follows $session = JFactory::getSession(); $session->get('freegeoip_ip');

Available session variables are:

freegeoipip
freegeoipcountrycode
freegeoipcountryname
freegeoipregioncode
freegeoipregionname
freegeoipcity
freegeoipzipcode
freegeoiplatitude
freegeoiplongitude
freegeoipmetrocode
freegeoiparea_code

API usage is limited to 10,000 queries per hour. After reaching this limit, all requests will result in HTTP 403 (Forbidden) until the roll over.

Visit freegeoip.net for more information on their service and how you can host your own instance of this system.