Google's now supporting "rich snippets" on shopping (e-commerce) sites in the U.S! For those not familiar, "rich snippets are search results that've been enhanced using structured data from your web pages." The new format shows price, availability, and product reviews on pages offering a product for sale.
The rich snippet display can make a fairly compelling case for click-throughs with the inclusion of pricing and availability right below the page link.
If you already give Google a Merchant Center feed, you're already this close to having your pricing, availability, and product reviews show up as rich snippets. You just need to add the rel="canonical" to your pages. The other way to get on board is to manually add the right markup to your pages.
Google will be rolling out rich snippets "soon" outside the U.S.
More Info: Help Page