Instead of scouring the web yourself for many products, you can use a new type of searcher called a "bot" ( as in robot). These are sites that will either go through the web, search engines or their own databases to find you the lowest price an any item. Some are general and others specialize in one or a few categories. Now what we need is a bot to go through all of these bots.
Alphabetical:
BookBlvd , BookFinder , Bottomdollar , Mysimon , PlanetRetail , PriceScan , Shopfind , webmarket ,yahoo shopping