Add taxonomy navigation to the WordPress admin toolbar

gistfile1.aw

<?php

add_action( 'admin_bar_menu', 'pjh_add_taxonomies_to_toolbar', 999 );

function pjh_add_taxonomies_to_toolbar( $wp_admin_bar )
{
	// check permissions
	if( ! current_user_can( 'manage_categories' ) ) return;

	global $wp_taxonomies;	

	// for each taxonomy
	foreach( $wp_taxonomies as $taxonomy => $tax_data )
	{
		// skip non-hierarchical taxonomies
		if( ! is_taxonomy_hierarchical( $taxonomy ) ) continue;

		// skip specific taxonomies
		// if( in_array( $taxonomy, array( 'genre', 'country' ) ) ) continue;

		$tax = get_taxonomy( $taxonomy );
		$url = admin_url( '/edit-tags.php?taxonomy=' . $tax->name );

		// get terms
		$tax_terms = get_terms( $taxonomy, 'number=9999&orderby=count&order=DESC&hide_empty=1' );		

		// limit number of terms added to toolbar
		// $tax_terms = array_slice( $tax_terms, 0, 10 );

		// add parent nodes to toolbar
		$wp_admin_bar->add_node( array(
			'id' => $tax->name,
			'title' => $tax->labels->name,
			'href' => $url,
			'meta' => array(
				'class' => $tax->name . '-toolbar-page',
				'title' => $tax->labels->name
			),
			'parent' => false
		) );			

		// for each term in taxonomy
		foreach( $tax_terms as $array => $data )
		{
			// determine parent and set up variables
			if( $data->parent != 0 ) :
				$term = get_term( $data->term_id, $taxonomy );
				$parent_term = get_term( $data->parent, $taxonomy );
				$parent = $parent_term->name;
				$link = get_term_link( $term );
			else :
				$parent = $tax->name;
				$term = get_term( $data->term_id, $tax->name );
				$link = get_term_link( $term );
			endif;

			$name = esc_attr( $data->name );
			$count = $data->count;	 

			// add additional query arguments
			// $query_arg = array( 'foo' => 'bar', 'baz' => 'qux' );

			// add subitems to parents
			$wp_admin_bar->add_node( array(
				'id' => $name,
				'title' => $name . ' (' . $count . ')',
				'href' => $link,
				//'href' => add_query_arg( $query_arg, untrailingslashit( $link ) ), // add additional query arguments
				'meta' => array(
					'class' => $name . '-toolbar-page',
					'title' => $data->description
				),
				'parent' => $parent
			) );
		}
	}
}

Paste the snippet in the functions.php file of your theme and adjust to your liking.

Notes

• Toolbar nodes will only be added if the current user can manage categories. Comment out line 6 (and take care of line 20) to enable for all logged in users.
• Only hierarchical taxonomies (categories, …) will be added to the toolbar. Comment out line 14 if you wish to display non-hierarchical taxonomies (post tags, …) as well.
• To exclude specific taxonomies uncomment and configure line 17.
• Terms are ordered by post count, and empty taxonomy terms (post count 0) are not shown. To return all items, change the value of hide_empty on line 23 to 0.
• Number of items shown is unlimited. You can limit the number of items that will be added to the toolbar with array_slice on line 26.
• If you would like to add extra query arguments, take a look at lines 59 and 66.
• This snippet requires WordPress 3.3 or higher