Scientific Seller provides keyword suggestions for Amazon listings and PPC ads, generated from an initial seed word or phrase.
The results list connected keywords, with related search suggestions for each.
A free Amazon keyword tool is available on their website, but to you need to sign up and create an account to see more results, perform more searches per day, export and save searches, or search outside of the United States.
Free limited tool available on the website. Full access costs from $29.99 to $49.99 per month.