I was just doing the same thing myself today!
$uploadDir = '/home/httpd/YOURSITE.com/httpdocs/DIRECTORY';
if ($handle = opendir($uploadDir)) {
while (false !== ($file = readdir($handle))) {
if ($file != "." && $file != "..") {
echo "<b><a href='http://www.YOURSITE.com/DIRECTORY/" . $file . "'>" . $file . "</a></b><p>";
}
}
closedir($handle);
}