AmazonWatcher lets you keep an eye on Amazon prices from your desktop. The great thing about it is that you can use it both to check for current prices on Amazon and to monitor those prices over time to see when they go down or when an item that was not inn stock previously is back in stock. This app can browse the US, UK, Germany, France, Japan and Canada Amazon websites.
You can add items to your "watch list" by either pasting the Amazon URL or using the built-in search function. The latter works extremely well, and each search result shows the list price, the Amazon price, prices from third-party vendors and even used prices. After you add an item, you can configure how the item will be monitored down at the "what to watch" pane. You can watch for price drops or for when an item is back in stock. Below that is the "How to React" pane. This basically establishes what the app will do when there is a change in the item's parameters. You can set the app to bring up the item webpage, put the product in your cart and take you to checkout, or send you an e-mail.
In short, AmazonWatcher is an excellent app for Amazon users. It works great, it is free and looks awesome.