If you like to shop at Amazon, you really should be using camelcamelcamel. This service tracks prices at Amazon and allows you to set alerts to tell you when prices drop on items you want to buy.
Here is a real world example: My wife and I wanted to buy some dishes that, at $76.48 per place setting, are quite a bit more than we are used to paying for dishes. We set a price alert and sat back to wait for the price to fall. Fast forward a month or so, and I got an email letting me know that the price dropped to $58.62, a savings of over $18 (counting taxes) per place setting. It took almost no effort on my part, just a few moments to copy and paste a URL to camelcamelcamel.
They even have a handy Chrome extension called the Camelizer. It adds a button to all Amazon pages that, when clicked, shows you price history and lets you set a price alert.
This works for pretty much anything that you know you want to buy, but don’t really need immediately. I’ve successfully used it to save money on new smoke detectors (the old ones still worked, they were just close to the expiration date), several books, a mattress for my daughter, a NAS, and more.
They also have a version for Best Buy. I don’t shop there so can’t really vouch for it, but looks like it works the same as the Amazon version.