User 'restrict_manage_posts' filter to add another filter. Use the following code in functions.php
function kc_add_taxonomy_filters() {
global $typenow;
// an array of all the taxonomyies you want to display. Use the taxonomy name or slug
$my_taxonomies = array( 'post_tag' );
switch($typenow){
case 'post':
foreach ($my_taxonomies as $tax_slug) {
$tax_obj = get_taxonomy($tax_slug);
$tax_name = $tax_obj->labels->name;
$terms = get_terms($tax_slug);
if(count($terms) > 0) {
echo "<select name="$tax_slug" id='$tax_slug' class="postform alignleft actions">";
echo "<option value="">Show All $tax_name</option>";
foreach ($terms as $term) {
echo '<option value="', $term->slug,'" ',selected( @$_GET[$tax_slug] == $term->slug , $current = true, $echo = false ) , '>' , $term->name ,' (' , $term->count ,')</option>';
}
echo "</select>";
}
}
break;
}
}
add_action( 'restrict_manage_posts', 'kc_add_taxonomy_filters' );