This Amazon Keyword Research Guide from Seller Sonar blog teaches you why is Amazon keyword research important and how to conduct efficient keyword research.
Amazon Key Word Tool Dominator
This Amazon keyword tool lets you filter countries and chooses a department. Note that the free version is limited to 2 searches per day.
Ranking & Index Checker
The Amazon Keyword Ranking & Index Checker is a Chrome extension that helps you check your current Amazon keyword ranking, indexing information, and page rank and monitor the effectiveness of your marketing efforts.
Scientific Seller is an effective keyword research tool for Amazon sellers by pulling all the keywords buyers are searching for from Amazon's search bar auto-complete system.