So here is quick tip if you have no idea what physical product to promote. Head over to www.google.com/products Everytime you refresh you get a new list of products.
I was just there now and never realised there was such a thing as a bed wetting alarm. That could be an interesting niche
I just wanted to add I'll use this if I get bored with Amazons bestseller list and then I'll just plug the products into the Google keyword search tool.