CamelCamelCamel[0] actually does some price tracking, but I'm not very familiar with what they do with it (with regard to giving advice on whether to buy or not). You might be able to grab some information from them on products via an API or scraper. I'm not seeing an API, nor do I see anything about using their data for other stuff, but I suppose it goes without saying that a really aggressive scraper wouldn't be welcome.
