We operate a powerful brand tracking system to monitor branded products sold on Amazon. If you're a brand looking to protect your products, check out www.semantics3.com
We built this neat little app using our new Push notifications API. It allows you to set up price push notifications on any product sold online, regardless of retailer.
Check it out here: www.semantics3.com/products/push
We've been secretly working on a much more industrial-scale version of this, with a focus on getting price updates for eCommerce products.
Basically you can register a product URL, select the price change event that matters to you, and we'll push it to you via our Push Notifications API.
Its been in the works for a while, but we have MASSIVE scale.
Our database is >60 million, and you can get price change push notifications on any of them.
Pretty useful if you're building your own shopping app and want the latest prices! It also helps, especially if you're trying to keep up with Amazon's pricing games.
Semantics3 (www.semantics3.com) has been tracking Amazon for almost 2 years now (we have price histories to boot!). We can, and do still offer price comparison functionality for products sold on Amazon; you can also compare these prices against other domains.