The Better Together Contribution is availalble at

This contribution allows you to associate products for discounts when they are purchased together, in the same way that Amazon does. It is an order total module, so you will see the discount at checkout time on page 2. Because of dependancies on the latest shopping_cart.php, you *must* be running ZenCart 1.3.5 to run this module.

More information is provided at:

Good luck,