BusinessWeek about PriceGrabber:

"PriceGrabber.com boasts 16 million unique users, 10.5 million products in its database, and 6,500 merchant clients [...]
We started what is called SKU association. We basically bundled or associated all these products — they’re identical with each other together. And then we would say: O.K., here are the product results that we have.
Other examples are bottom-line price: The inclusion of tax and shipping. This is something that we’ve had almost since inception, about five-and-a-half years ago, and, of course, that’s something others have introduced more recently.
We also have what we call product tours. It gives you 3-D pictures of the products and more detail. Another differentiator is we will tell shoppers if a product is "refurbished.""