function list_hooked_functions($tag=false){
    global $wp_filter;
    if ($tag) {
        $hook[$tag] = $wp_filter[$tag];
        if (!is_array($hook[$tag])) {
            trigger_error("Nothing found for '$tag' hook", E_USER_WARNING);
            return;
        }
    } else {
        $hook = $wp_filter;
        ksort($hook);
    }
    echo '<pre>';
    foreach($hook as $tag => $priority){
        echo "<br />&gt;&gt;&gt;&gt;&gt; <strong>$tag</strong><br />";
        ksort($priority);
        foreach($priority as $priority => $function){
            echo $priority;

            foreach($function as $name => $properties)
                echo " ".$name."<br />";

        }
    }
    echo '</pre>';
    return;
}

list_hooked_functions('wp_head');