This PHP code is designed to work on servers running the latest version of PHP as well, unlike most of the code samples on the web which will not work on many servers because of a checksum error.

<?php
//PageRank Lookup v1.1 by HM2K (update: 31/01/07)
//based on an alogoritham found here: http://pagerank.gamesaga.net/
 
//settings - host and user agent
$googlehost='toolbarqueries.google.com';
$googleua='Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.0.6) Gecko/20060728 Firefox/1.5';
 
//convert a string to a 32-bit integer
function StrToNum($Str, $Check, $Magic) {
    $Int32Unit = 4294967296;  // 2^32
 
    $length = strlen($Str);
    for ($i = 0; $i < $length; $i++) {
        $Check *= $Magic;      
        //If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31),
        //  the result of converting to integer is undefined
        //  refer to http://www.php.net/manual/en/language.types.integer.php
        if ($Check >= $Int32Unit) {
            $Check = ($Check - $Int32Unit * (int) ($Check / $Int32Unit));
            //if the check less than -2^31
            $Check = ($Check < -2147483648) ? ($Check + $Int32Unit) : $Check;
        }
        $Check += ord($Str{$i});
    }
    return $Check;
}
 
//genearate a hash for a url
function HashURL($String) {
    $Check1 = StrToNum($String, 0x1505, 0x21);
    $Check2 = StrToNum($String, 0, 0x1003F);
 
    $Check1 >>= 2;      
    $Check1 = (($Check1 >> 4) & 0x3FFFFC0 ) | ($Check1 & 0x3F);
    $Check1 = (($Check1 >> 4) & 0x3FFC00 ) | ($Check1 & 0x3FF);
    $Check1 = (($Check1 >> 4) & 0x3C000 ) | ($Check1 & 0x3FFF); 
       
    $T1 = (((($Check1 & 0x3C0) << 4) | ($Check1 & 0x3C)) <<2 ) | ($Check2 & 0xF0F );
    $T2 = (((($Check1 & 0xFFFFC000) << 4) | ($Check1 & 0x3C00)) << 0xA) | ($Check2 & 0xF0F0000 );
       
    return ($T1 | $T2);
}
 
//genearate a checksum for the hash string
function CheckHash($Hashnum) {
    $CheckByte = 0;
    $Flag = 0;
 
    $HashStr = sprintf('%u', $Hashnum) ;
    $length = strlen($HashStr);
       
    for ($i = $length - 1;  $i >= 0;  $i --) {
        $Re = $HashStr{$i};
        if (1 === ($Flag % 2)) {              
            $Re += $Re;    
            $Re = (int)($Re / 10) + ($Re % 10);
        }
        $CheckByte += $Re;
        $Flag ++;       
    }
 
    $CheckByte %= 10;
    if (0 !== $CheckByte) {
        $CheckByte = 10 - $CheckByte;
        if (1 === ($Flag % 2) ) {
            if (1 === ($CheckByte % 2)) {
                $CheckByte += 9;
            }
            $CheckByte >>= 1;
        }
    }
 
    return '7'.$CheckByte.$HashStr;
}
 
//return the pagerank checksum hash
function getch($url) { return CheckHash(HashURL($url)); }
 
//return the pagerank figure
function getpr($url) {
        global $googlehost,$googleua;
        $ch = getch($url);
        $fp = fsockopen($googlehost, 80, $errno, $errstr, 30);
        if ($fp) {
           $out = "GET /search?client=navclient-auto&ch=$ch&features=Rank&q=info:$url HTTP/1.1\r\n";
           //echo "<pre>$out</pre>\n"; //debug only
           $out .= "User-Agent: $googleua\r\n";
           $out .= "Host: $googlehost\r\n";
           $out .= "Connection: Close\r\n\r\n";
       
           fwrite($fp, $out);
           
           //$pagerank = substr(fgets($fp, 128), 4); //debug only
           //echo $pagerank; //debug only
           while (!feof($fp)) {
                        $data = fgets($fp, 128);
                        //echo $data;
                        $pos = strpos($data, "Rank_");
                        if($pos === false){} else{
                                $pr=substr($data, $pos + 9);
                                $pr=trim($pr);
                                $pr=str_replace("\n",'',$pr);
                                return $pr;
                        }
           }
           //else { echo "$errstr ($errno)<br />\n"; } //debug only
           fclose($fp);
        }
}
 
//generate the graphical pagerank
function pagerank($url,$width=40,$method='style') {
        if (!preg_match('/^(http:\/\/)?([^\/]+)/i', $url)) { $url='http://'.$url; }
        $pr=getpr($url);
        $pagerank="PageRank: $pr/10";
 
        //The (old) image method
        if ($method == 'image') {
        $prpos=$width*$pr/10;
        $prneg=$width-$prpos;
        $html='<img src="http://www.google.com/images/pos.gif" width='.$prpos.' height=4 border=0 alt="'.$pagerank.'"><img src="http://www.google.com/images/neg.gif" width='.$prneg.' height=4 border=0 alt="'.$pagerank.'">';
        }
        //The pre-styled method
        if ($method == 'style') {
        $prpercent=100*$pr/10;
        $html='<div style="position: relative; width: '.$width.'px; padding: 0; background: #D9D9D9;"><strong style="width: '.$prpercent.'%; display: block; position: relative; background: #5EAA5E; text-align: center; color: #333; height: 4px; line-height: 4px;"><span></span></strong></div>';
        }
       
        $out='<a href="'.$url.'" title="'.$pagerank.'">'.$html.'</a>';
        return $out;
}
 
//if ((!isset($_POST['url'])) && (!isset($_GET['url']))) { echo '<form action="" method="post"><input name="url" type="text"><input type="submit" name="Submit" value="Get Pagerank"></form>'; }
if (isset($_REQUEST['url'])) { echo pagerank($_REQUEST['url']); }
?>