A useful free tool you can use to help with keyword research is Google’s ‘Keyword Planner’. It is a tool which helps generate refined keyword lists for your website. Google offers great insight and tips on getting the most out of Keyword Planner and will help generate list of keywords which will form part of your SEO strategy.
To use it, you must have a google adwords account: http://www.google.com/adwords and from there it’s under tool’s & analysis in the settings.
The catch is, in order to use this feature you need a google adwords account, and to have one you have to pay for a campaign. So if you already have an account, then it’s a no brainer to use the free tools provided.