Answer The Public
Answer the public will produce a selection of phrases and questions for any given keyword. A very good tool for voice SEO.
This is a word cloud visualization tool. On way to use this would be to profile your competitors websites to generate keyword ideas.
Niche Laboratory collects data from the top results for your target search term and provides a list of keywords and phrases from those pages, and it produces a keyword cloud.
Designed for e-commerce, this toolis particularly useful for people that are selling on Amazon.
Merchant Words combines keyword data from Amazon a Google.
Seed keywords is a great tool for brainstorming