Все ключевые теги:
$result = mysql_query("SELECT `tags` FROM `$dle_category`
ORDER BY `date_modified` DESC");
while ($item = mysql_fetch_array($result))
$dump_string .= $item["tags"].",";
$dump_mas = explode(",", $dump_string);
while (list($key, $val) = each($dump_mas))
{ if (isset($mas[trim($val)]))
$mas[$val]++;
else
$mas[$val] = 1;
}
while (list($key, $val) = each($mas))
echo "$key";