Add select menu to filter by custom field in WordPress admin
http://wpsnipp.com/index.php/functions-php/add-select-menu-to-filter-by-custom-field-in-admin/ ...
Custom filter “sort” dropdown
http://wordpress.stackexchange.com/questions/45/how-to-sort-the-admin-area-of-a-wordpress-custom-post-type-by-a-custom-field ...