Eu uso isso no meu site, funciona bem e você pode apontar as ferramentas do Google para webmasters para "this_file.php" e funciona maravilhas!
<?php
header("Content-type: text/xml");
echo'<?xml version=\'1.0\' encoding=\'UTF-8\'?>';
echo' <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">';
include '../include.php';
$sql = mysql_query("select blah from bleh");
while ($string = mysql_fetch_array($sql)){?>
<url>
<loc>http://www.domain.com/dir/<?echo $string['value'];?>/index.php</loc>
<changefreq>weekly</changefreq>
</url>
<?php } ?>
</urlset>
