I use Amazon's Wish List not just so others know what to get me come birthdays and holidays, but also to track items I'm interested in buying for myself--once the price goes down, that is.
Unfortunately, Amazon won't notify me of price drops. Thankfully, Wish Radar will. This free service lets you set a target price for each item on your Wish List, then pings you via e-mail or text message when one hits it.
Wish Radar can also track individual items (i.e. stuff not on your list) and set you up with your own RSS feed (for easier monitoring of your "radar"). You can even text a UPC number (or ISBN number, in the case of books) from your phone and instantly get back pricing info from Amazon--a great way to see if there's a better deal online than what you're seeing in a store.
So, for example, I've got my eye on ATV-racing game Pure for the Xbox 360. Amazon's current price is a whopping $56.99, while the best deal on Amazon Marketplace is $41. When either one hits $30, Wish Radar will ping me so I can snap up the game. Meanwhile, I go about my business; it's a set-it-and-forget-it service. And a great one at that.