AMZScout - AMZScout extension will help you make a decision about picking a niche based on the actual data, not intuition.

Jungle Scout - Amazon product research made easy.

Inventory Spy - Spy how many products remain on any Amazon Product’s offer listing page.

ProfitGuru - ProfitGuru is the easiest way to find the most profits on Amazon.

Site Search 360 - Site Search 360 enhances and improves your built-in CMS or product search with autocompletion, semantic search, filters, facets, detailed analytics, and a whole lot of customization options.

Egrow - Egrow is a free web-based tool specifically developed for Amazon sellers.