As far as I know, the Amazon web services you're talking about can only be used if you're sending the customers back to Amazon to make purchases. I think you get a commission for this. (It wouldn't make sense from Amazon's point of view to let other applications use all their content without any return).

I've used that service in the past (not commercially though) and it's pretty straight forward to setup, but I'd check the terms of service first to see what's allowed.

I don't know of any other services that let you use their content like that....sorry!