Here is a PHP code snippet that will allow you to check the Alexa rank, and the number of inbound links in Google, MSN and Yahoo search engines.

All you need to do is set the $url variable, which you can do by posting from a form, or perhaps including it in the querystring.

<?php
/*
Function to check Alexa rank
*/

function get_alexa($url){
    $site = fopen('http://www.alexa.com/data/details/main?url='.urlencode($url),'r');
    while($cont = fread($site,1024657)){
        $total .= $cont;
    }
    fclose($site);
    $match_expression = '/for more information about the Alexa Web Information Service.-->(.*)<\/span><\/a>/Us';
    preg_match($match_expression,$total,$matches);
    return strip_tags($matches[1]);
}

/*
Function to check Google Backlinks
*/
function google_backs($url){
    $site = fopen('http://www.google.com/search?q=link%3A'.urlencode($url),'r');
    while($cont = fread($site,1024657)){
        $total .= $cont;
    }
    fclose($site);
    $match_expression = '/of about <b>(.*)<\/b> linking to/Us';
    preg_match($match_expression,$total,$matches);
    return $matches[1];
}

/*
Functin to check MSN Backlinks
*/
function msn_backs($url){
    $site = fopen('http://search.live.com/results.aspx?q=link%3A'.urlencode($url),'r');
    while($cont = fread($site,1024657)){
        $total .= $cont;
    }
    fclose($site);
    $match_expression = '/<h5>Page 1 of (.*) results<\/h5>/Us';
    preg_match($match_expression,$total,$matches);
    return $matches[1];
}

/*
Function to check Yahoo Backlinks (Called inlinks)
*/
function yahoo_backs($url){
    $site = fopen('http://siteexplorer.search.yahoo.com/search?p='.urlencode($url).'&bwm=i&bwmf=a&bwms=p','r');
    while($cont = fread($site,1024657)){
        $total .= $cont;
    }
    fclose($site);
    $match_expression = '/of about <strong>(.*) <\/strong>/Us';
    preg_match($match_expression,$total,$matches);
    return $matches[1];
}

/*
Example Usage:
*/
$link = 'http://www.google.com';
echo "URL: $link, Has ". get_alexa($link).' Alexa Rank, Google BackLinks: '.google_backs($link).' - MSN BackLinks '.msn_backs($link).' Yahoo BackLinks: '.yahoo_backs($link);

?>