For all those who want to edit the Sort By: Dropdown box on the featured/all/new products pages:

Open these 3 files: (where YOURS is the name of your template)
#1 includes/templates/YOURS/templates/tpl_modules_listing_display_order.php
#2 includes/modules/listing_display_order.php
#3 includes/languages/YOURS/english.php


Open #1 includes/templates/YOURS/templates/tpl_modules_listing_display_order.php

From what my beginner standpoint can tell, this pretty much contains the sort by: dropdown menu. Comment out unwanted options and add new ones. For example I took out price (because everything on my site is $5) and I added manufacturer option. I use <!-- --> but you might prefer to use the /** */ comments. Each option starts at <option value… and goes to </option>

Mine (edited) looks like:
Code:
<?php
/**
 * Module Template
 *
 * @package templateSystem
 * @copyright Copyright 2003-2006 Zen Cart Development Team
 * @copyright Portions Copyright 2003 osCommerce
 * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0
 * @version $Id: tpl_modules_listing_display_order.php 3369 2006-04-03 23:09:13Z drbyte $
 */
?>
<?php
// NOTE: to remove a sort order option add an HTML comment around the option to be removed
?>

<div id="sorter">
<label for="disp-order-sorter"><?php echo TEXT_INFO_SORT_BY; ?></label>
<?php
  echo zen_draw_form('sorter_form', zen_href_link($_GET['main_page']), 'get');
  echo zen_draw_hidden_field('main_page', $_GET['main_page']);
//  echo zen_draw_hidden_field('disp_order', $_GET['disp_order']);
  echo zen_hide_session_id();
?>
    <select name="disp_order" onchange="this.form.submit();" id="disp-order-sorter">
<?php if ($disp_order != $disp_order_default) { ?>
    <option value="<?php echo $disp_order_default; ?>" <?php echo ($disp_order == $disp_order_default ? 'selected="selected"' : ''); ?>><?php echo PULL_DOWN_ALL_RESET; ?></option>
<?php } // reset to store default ?>
    <option value="1" <?php echo ($disp_order == '1' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_NAME; ?></option>
    <option value="2" <?php echo ($disp_order == '2' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_NAME_DESC; ?></option>
  <!--<option value="3" <?php echo ($disp_order == '3' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_PRICE; ?></option>
    <option value="4" <?php echo ($disp_order == '4' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_PRICE_DESC; ?></option>
    <option value="5" <?php echo ($disp_order == '5' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_MODEL; ?></option>-->
    <option value="6" <?php echo ($disp_order == '6' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_MANUFACTURER; ?></option>
    <option value="7" <?php echo ($disp_order == '7' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_MANUFACTURER_DESC; ?></option>
    <option value="8" <?php echo ($disp_order == '8' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_DATE_DESC; ?></option>
    <option value="9" <?php echo ($disp_order == '9' ? 'selected="selected"' : ''); ?>><?php echo TEXT_INFO_SORT_BY_PRODUCTS_DATE; ?></option>
    </select></form></div>

Open #2 includes/modules/listing_display_order.php

You can add a case that correlates with whatever you want to add to the sort by: dropdown menu. I added an option m.manufacturers_name here. I'm not sure but there may be other options you can add here with it's p.product_whatever name.
Code:
 case ($_GET['disp_order'] == 6):
  $order_by = " order by m.manufacturers_name";
  break;
  case ($_GET['disp_order'] == 7):
  $order_by = " order by m.manufacturers_name DESC";
  break;
Open #3 includes/languages/YOURS/english.php

Scroll down to the section towards the bottom titled // sort order titles for dropdowns
. Add a line(s) that correlate with the TEXT_INFO_SORT_BY_WHATEVER lines that you may have added in the first file tpl_modules_listing_display_order.php.
For my example I added the manufacturer title (I call them artists because it's a CD site).
Code:
// sort order titles for dropdowns
  define('PULL_DOWN_ALL_RESET','- RESET - ');
  define('TEXT_INFO_SORT_BY_PRODUCTS_NAME', 'Album Name (A-Z)');
  define('TEXT_INFO_SORT_BY_PRODUCTS_NAME_DESC', 'Album Name (Z-A)');
  define('TEXT_INFO_SORT_BY_PRODUCTS_PRICE', 'Price - low to high');
  define('TEXT_INFO_SORT_BY_PRODUCTS_PRICE_DESC', 'Price - high to low');
  define('TEXT_INFO_SORT_BY_PRODUCTS_MODEL', 'Model');
  define('TEXT_INFO_SORT_BY_MANUFACTURER', 'Artist (A-Z)');
  define('TEXT_INFO_SORT_BY_MANUFACTURER_DESC', 'Artist (Z-A)');
  define('TEXT_INFO_SORT_BY_PRODUCTS_DATE_DESC', 'Date Added - New to