SmartMoney.com published a great review of the top online price comparison sites. For the most part I agree with their findings. Their reviews found PriceGrabber.com was the superior website for comparison shopping. One of the better features included on PriceGrabber.com is the ability to setup alerts for products based on your desired price range. With the constantly declining costs of technology products, it doesn't make sense to pay bleeding edge prices.
They also rated Yahoo! Shopping, Shopping.com and NexTag as good sites. Rated towards the bottom was Google Products (AKA Google Shopping) because it provided poor details on listings. In their defense, Google says the tool is simply a way to find products and the stores that sell them.
Regardless of what online tool you use, now there is no excuse of overpaying for any product. My advice to you when using these price comparison tools is to perform searches by the part number of the product you want. For example, if I know that I want a specific 3Com network switch, I look up the part number on 3Com's website then I plug that part number into PriceGrabber.com. This ensures that I get the exact item I am looking to buy.