Look at the API from hostip.info - it provides lots of information.
Example in PHP:
$data = file_get_contents("http://api.hostip.info/country.php?ip=12.215.42.19");
//$data contains: "US"
$data = file_get_contents("http://api.hostip.info/?ip=12.215.42.19");
//$data contains: XML with country, lat, long, city, etc...
If you trust hostip.info, it seems to be a very useful API.
