CamelCamelCamel.com is a handy price tracking tool that lets you see how far a product's price has dropped in the past. While hundreds of Amazon items are constantly on sale, their prices often fluctuate over time. Even if something is a few dollars off now, CamelCamelCamel will let you know the item's lowest lifetime price so you can judge the deal before you buy.
For example, I recently saw a Hamilton Beach blender on sale for about 20% off, which isn't bad, but checking CamelCamelCamel showed that the same blender was selling for nearly 50% off just a few weeks earlier.
To save yourself some time, you can install the CamelCamelCamel browser extension to get the price tracking information whenever you visit an Amazon product page. As an added bonus, CamelCamelCamel will let you set price alerts so you'll automatically receive an email when a product hits the price you want.