Just up on the MSN Shopping Insider is a post about some new and useful features that have gone live at MSN Shopping. Now, it's possible to focus and refine a shopping search using attributes that are specific to the product category your searching in. This has been possible with MSN Shopping in the past with categories like televisions and computers but as of today these types of refinements are available in more than 300 categories. For example, if you're searching for flowers, you can now focus your flower search by type (roses, lillies, etc), arrangement type (bouquet, vase, planter, etc.) flower color, and seller. Of course, you can also focus by price range. If you're searching for a diamonds, you can refine by color, carat, clarity, cut and price. Little to no learning curve to use these refinements. A good example of keeping it simple.
I didn't check all 300 categories (-:, but I did look at other shopping engines to see what refinements they offer shopping for diamonds.
+ Shopzilla also allows to refine by stone shape, carat, cut, color, clarity, and price range.
+ Shopping.com allows a searcher to refine a search for diamonds by clarity, carat, and price. Very similar to MSN Shopping.
+ PriceGrabber offers a carat refinement.
+ Yahoo Shopping, refine by price.
+ Become.com, refine by price.
+ Froogle, refine by price and store