TitleZ is a new (Atlas-based) web application that uses the Amazon Historical Pricing web service to generate historical reports on an Amazon title or search.
TitleZ has a simple and clean interface, and generates good-looking reports (using data from Amazon ECS as well). It's free for now, but they plan to charge after the beta period is over. Also, links from TitleZ to Amazon products use TitleZ's affiliate code, so that's part of their revenue model as well.
This is a nice implementation of an application Amazon obviously had in mind when they made the Historical Pricing web service available.