News from the Yahoo Developer Network today that they've just released an API for Yahoo Shopping. Details and documentation are posted here.
With the Product Search API, developers can search by keyword (product names); limit the search to a specific merchant, price range or product category, and filter merchants according to their Yahoo! User ratings. The Price Comparison Grid API gives developers access to millions of products offered by multiple merchants, returning base price, tax and shipping info and total price (based on zip code).