Sortable custom field values from all posts on a page template

What if you use ORDER BY pm.meta_value ASC in WP db class:

$r = $wpdb->get_col( $wpdb->prepare( "
        SELECT pm.meta_value FROM {$wpdb->postmeta} pm
        LEFT JOIN {$wpdb->posts} p ON p.ID = pm.post_id
        WHERE pm.meta_key = '%s' 
        AND p.post_status="%s" 
        AND p.post_type="%s"
        ORDER BY pm.meta_value ASC
        ", $key, $status, $type ) );

That will provide you an ASCending ordered array.