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 than 5 searches per day, export and save searches, or search outside of the United States.
Free limited tool available on the website with Seller upgrade account for unlimited searches $19.99 per month.
Full access costs from $29.99 to $49.99 per month.