Over the summer, Clark mentioned a service for airline customers called Yapta.com. Yapta lets you know if you're eligible for a refund or credit if airfare drops after you've made a purchase.

Most major U.S. airlines will give you a voucher for the difference if you ask. The only two I know of that don't are Allegiant and Frontier.

Each airline picks a price point at which they’ll dole out. For Alaska Airlines, JetBlue, and Southwest, you’ll get a refund for any price drop whatsoever. For American, Delta, United, Continental, and US Airways, however, the price drop has to be $150 or more before they’ll shell out.

But unless you religiously follow airfares after you’ve made your purchase, you might not even know that you’ve overpaid. That’s where something like Yapta comes in handy. After completing the free registration, Yapta will e-mail you when your flight goes down in price and help you get a refund for the difference.

One caveat here, though. Some airlines will charge big fees if you want to process a refund. American, Delta, United, Continental, and US Airways all assess a whopping $150 for domestic flights and more for international ones. So make sure it’s worth your while before you get involved.

Meanwhile, now that same idea is being applied to the world of retail. Many stores offer a price-protection policy. So if you buy something and the price drops within 30 days, the retailer may give you a refund. But who's really combing over circulars and online ads after you've made your purchase?

Enter the magic of the Internet. There are a couple of free, ad-supported websites that will do it for you! They include RefundPlease.com and PriceProtectr.com. You simply enter the make and model of what you bought and they'll send you an e-mail if the price drops.

PriceProtectr.com claims to have saved consumers more than $500,000, while RefundPlease.com says its savings are more in the $100,000 range.