I've been using http://freegeoip.net/

It's not perfect, but it seems to be good enough for my purposes.

     $ip = $_SERVER['REMOTE_ADDR'];
     $ua = $_SERVER['HTTP_USER_AGENT'];
        $ch = curl_init();
        // set url
        curl_setopt($ch, CURLOPT_URL, "freegeoip.net/csv/"    . $ip);
        //return the transfer as a string
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        // $output contains the output string
        $ip = curl_exec($ch);
        // close curl resource to free up system resources
        curl_close($ch);    
     $array = explode(',', $ip);