Amazon has released Windowshop for iPad. If you use Amazon as frequently as I do, you may already realize that the current iPhone and iPad offerings are pretty grim. I've never been a huge fan of the Amazon app as it seems to just be a mobile version of the site shoved into an app. Windowshop seems to bridge that gap quite nicely on the iPad and it's now available in the App Store as a free download.
It does an extremely nice job of separating categories and allowing you to quickly switch between them. To me, this is a lot less tedious compared to weeding through search results and refining them. Your categories will simply appear at the top and you'll be presented with columns of search results. From there, you can simply pick the best category at the top that best suits what you're looking for and just search within that section. If they could make a scaled down version of this for the iPhone as well, I'd be all set! Pick it up and give it a shot, and of course, let us know what you think!