We recommend Google keyword finder - it is the most popular tool for KW analysis, it is basing on Google search statistics, it is available for anyone who has an Adwords account.
What is more, there are lots of other free tools that you can use, e.g.: Google Trends, Google Auto Suggest Keyword Tool, UbberSuggest, Wordtracker,
Keywordtool.io., KWfinder, LongtailPro, SEMrush, etc...