Keyword research is by far the most important part of any search engine optimization campaign and not all keyword research tools are created equal. For the most part you can get good data from most of the tools that have already been suggested; however, you may not have the filtering capabilities that allow you to narrow down which keywords are actually worth trying to rank for. A few important things you need to look for when researching keywords is whether or not the keyword is relevant with the content on your your site, does the keyword have a good amount of traffic (searches per month), does the keyword have commerciality and the keyword your trying to rank for is not too competitive. A keywords tool like Market Samurai makes finding these types of keywords a very simple process saving you a massive amount of time and finding you keywords that you can actually rank for fairly easy.