We've mentioned browser extensions to help you shop before, but this one targets Google Chrome and Firefox users (but there are Internet Explorer and Safari versions available). Since a lot of people shop online, it's very convenient to have your browser suggest comparable products at other retailers, allowing you to see if you are getting a good deal.
Previously, we've mentioned The Invisible Hand extension for Firefox that works for Amazon, but for over 50 U.S. and UK retailer sites. A subtle drop-down bar tells you if you've got the best price on the Web. BuyLater does something similar, but for Amazon exclusively.
PriceBlink is also a browser extension that's supposed to optimize your shopping experience. It's good that these add-ons are unobtrusive and hidden away when not in use. PriceBlink lets you know if you've found the lowest price around, including shipping and available coupons. The Firefox version also has a wish list feature, allowing you to list your upcoming purchases, categorize them, and add price alerts to let you know when the price drops. The Chrome version is available here while the Firefox add-on is here.
The thing that sets PriceBlink apart from the other extensions is that it has access to a bunch of coupons as well, from well-known retailers like BestBuy and Sears. If you stack these with the deals that you can find, then you are going to save some money while you shop.