Google keyword tool is one of the best & its free too... If you are not sure what keyword to find suggestions for then just use the url of your competitors website & the tool will do the rest for you Its always recommended to choose the keywords with low competition & high search volume, though its a time consuming process but the results are Good
Google Keyword Tool. https://adwords.google.com/o/Target...000&ideaRequestType=KEYWORD_IDEAS#search.none ^^ That's what I use and all I need. That and Google search. Market Samurai is one of the best paid, but there are literally tons out there to try and buy.