Zen Cart Discount Chooser (also known as Free Gift Chooser) is a great way to create cross-selling promotions (Buy product A, get product B at a discount) for your shopping cart. However, because the configurability of the promotions has so many possibilities, I was never able to create a module like Better Together Checkout Candy for Zen Cart, which notices that A is in the cart and prompts the customer to buy B.
Because I recognized that customers needed some sort of promotional mechanism, I created Big Upsell for Zen Cart, which shows the available offers on the Shopping Cart and Checkout Shipping pages. Using Big Upsell, in conjunction with Discount Preview (which shows the discount once the customer has purchased all the components of the promotion), allows you to more effectively promote the discounts you have created.