functions.php

<?php
/*
Description: Adds a taxonomy filter in the admin list page for a custom post type.
Written for: http://wordpress.stackexchange.com/posts/582/
By: Mike Schinkel - http://mikeschinkel.com/custom-workpress-plugins
Instructions: Put this code in your theme's functions.php file or inside your own plugin. Edit to suite your post types and taxonomies. Hope this helps...
*/

//
add_filter('manage_{custom_post_type_name}_posts_columns', 'add_custom_taxonomy_column');
function add_custom_taxonomy_column( $posts_columns ) {
	if (!isset($posts_columns['author'])) {
		$new_posts_columns = $posts_columns;
	} else {
		$new_posts_columns = array();
		$index = 0;
		foreach($posts_columns as $key => $posts_column) {
			if ($key=='author') {
			$new_posts_columns['{column_name}'] = null;
			}
			$new_posts_columns[$key] = $posts_column;
		}
	}
	$new_posts_columns['{column_name}'] = '{Column pretty name}';
	return $new_posts_columns;
}


// manage_pages_custom_column for hierarchical custom post type
// manage_posts_custom_column otherwise
add_action('manage_posts_custom_column', 'display_taxonomy_terms',10,2);
function display_taxonomy_terms($column_id,$post_id ) {
	global $typenow;
	if ($typenow=='{cutom_post_type_name}') {
		$taxonomy = '{custom_taxonomy_name}';
		switch ($column_id) {
		case '{column_name}':
			$custom_terms = get_the_terms($post_id,$taxonomy);
			if (is_array($custom_terms)) {
				foreach($custom_terms as $key => $custom_term) {
					$edit_link = get_term_link($custom_term,$taxonomy);
					$custom_terms[$key] = '<a href="'.$edit_link.'">' . $custom_term->name . '</a>';
				}
				echo implode(' | ', $custom_terms);
			}
			break;
		}
	}
}


/* JUST AN HYPOTHETICAL EXAMPLE
add_action('manage_posts_custom_column', 'manage_posts_custom_column',10,2);
function manage_posts_custom_column( $column_id,$post_id ) {
	global $typenow;
	switch ("{$typenow}:{$column_id}") {
	case 'listing:business':
		echo '...whatever...';
		break;
	case 'listing:property':
		echo '...whatever...';
		break;
	case 'agent:listing':
		echo '...whatever...';
		break;
	}
}
*/

add_action('restrict_manage_posts','restrict_custom_post_type_by_taxonomy');
function restrict_custom_post_type_by_taxonomy() {
	global $typenow;
	global $wp_query;
	if ($typenow=='{custom_post_type_name}') {
		$taxonomy = '{custom_taxonomy_name}';
		$business_taxonomy = get_taxonomy($taxonomy);
		wp_dropdown_categories(array(
			'show_option_all' =>  __("Show All {$business_taxonomy->label}"),
			'taxonomy'        =>  $taxonomy,
			'name'            =>  '{custom_taxonomy_name}',
			'orderby'         =>  'name',
			'selected'        =>  $wp_query->query['term'],
			'hierarchical'    =>  true,
			'depth'           =>  3,
			'show_count'      =>  true,  // This will give a view
			'hide_empty'      =>  true,   // This will give false positives, i.e. one's not empty related to the other terms. TODO: Fix that
		));
	}
}
add_filter('parse_query','convert_term_id_to_taxonomy_term_in_query');
function convert_term_id_to_taxonomy_term_in_query($query) {
	global $pagenow;
	$qv = &$query->query_vars;
	if ($pagenow=='edit.php' &&
			isset($qv['taxonomy']) && $qv['taxonomy']=='{custom_taxonomy_name}' &&
			isset($qv['term']) && is_numeric($qv['term'])) {
		$term = get_term_by('id',$qv['term'],'{custom_taxonomy_name}');
		$qv['term'] = $term->slug;
	}
}

//add_action('init','register_listing_post_type');
//function register_listing_post_type() {
//	register_post_type('listing',array(
//		'label' => 'Listings',
//		'public' => true,
//		'publicly_queryable' => true,
//		'show_ui' => true,
//		'query_var' => true,
//		'rewrite' => true,
//		'capability_type' => 'post',
//		'hierarchical' => false,
//	));
//}
//add_action('init','register_business_taxonomy');
//function register_business_taxonomy() {
//	register_taxonomy('business',array('listing'),array(
//		'label' => 'Businesses',
//		'public'=>true,
//		'hierarchical'=>true,
//		'show_ui'=>true,
//		'query_var'=>true
//	));
//}