There are many keyword planner tools available and most of them are free. I have used and liked :
(1) Google AdWords : keyword planner. And
(2) Adword & SEO keyword Permutation Generator.
You can try other tools also, like:
(1) Google Correlate.
(2) IMforSMB Bulk Keyword Generator
(3) Keyword In
(4) Soovle
(5) Ubersuggest