Pricehare is a tool which will track price changes in products.
A few months ago I released Pricehare, a simple tool which will email you when the price drops on a product you are watching.
I came up with the idea after repeatively visiting a website to check the price of a product. I then wrote a small script which would do this for me, notifying me when the content of the page changed. This initially concept worked really well, I managed to save 25% in a few days because of a flash sale. From this inital concept I built a much smarter algoritum which is able to automatically find the price on a page.
All you need to get started is a URL and an email address.
Pro Tip - It quickly proved way to complicated to add everything I was looking at via URL so I also created a small bookmarklet a tiny JS bookmarket which will automatically add a watch for the page your on.