I've been trying to figure out Amazon's Browse Nodes and how their salesrank really works so I put together a very quick and dirty Amazon mash-up. It's Ajax approved, full of JSON-y goodness, and even uses XSL!
Try it at: http://texsy.com/amazonCats.php - remember - it's just a hack I built for research, but it's kinda fun.
If you click on "Baby", you'll see the top selling baby products at Amazon, and you can refine. Some categories don't show any results, however.