There are many SEO tutorials that point us to keyword tools that no longer exist, an example is the overture keyword tool, which is long gone. Such is the dynamic nature of the web that no SEO practice remains the same for a long time.
However there are a few services that are still free and functional, so utilize them to maximize your growth, here it goes, in no particular order:
Google Keyword Tool : The tool shows you top 100 keyword related to your niche, also requires a captcha authentication, but if you have an adwords account, you don’t need to enter the captcha verification and full list of keywords will be shown, Its therefore recommended that you sign up for adwords, and get a $100 or $75 credit on adwords as well.
WordTracker : Wordtracker is the tool that most affiliate marketers and professional bloggers use, its good but most of it’s services are not free, you can get a limited amount of value from it free service too.
Bing Webmasters Tools : The famous overture keyword tool was acquired by Yahoo! And after that Yahoo! And Bing now offers a free keyword tool in their inventory.
There maybe a few good free tools still “out there”, but the above three generally dominate the market and it’s sufficient for general keyword building process.
There is also one more technique that we use, using google search itself. We enter broad keywords related to our niche and wait for the input box to display the autocomplete drop down, with many other keyword suggestions. Also down below the results there are more keywords named “related searches”