Ultrasuggest

Generate hundreds of other related keywords based on a single keyword that users are actually searching.
Displays suggestions from the Google, Yandex, Amazon, YouTube, eBay, Wikipedia, Yahoo, Google Shopping, Google News, and Bing search fields.
Plus, all possible variations for all letters and numbers.
the Keyword Tool does it faster than you could ever analyze it yourself :)
also available as SEO API or Whitelabel SEO Tool