Filter posts (or CPTs) by a custom taxonomy in Admin.

functions-filter-taxonomy.php

	function product_category_filter() {
		global $typenow;
		if ($typenow == 'product') :
			$args = array(
				'show_option_all'	=> "Show All Categories",
				'taxonomy'			=> 'product_category',
				'name'				=> 'product_category',
				'value_field'		=> 'slug',
				'selected'			=> !empty( $_GET['product_category'] ) ? $_GET['product_category'] : null
			);
			wp_dropdown_categories($args);
		endif;
	}

	function product_filter_request( $request ) {
		if (is_admin() && $GLOBALS['PHP_SELF'] == '/wp-admin/edit.php' && isset($request['post_type']) && $request['post_type'] == 'product') {
			$term				= get_term( $request['product_category'], 'product_category' );
			$request['term']	= $request['product_category'];
		}
		return $request;
	}
	
	function __construct() {
		parent::__construct();
		add_action( 'restrict_manage_posts', array( &$this, 'product_category_filter' ) );
		add_action( 'request', array( &$this, 'product_filter_request' ) );
	}