One of my favorite subjects to teach on at our live SEO Mastery Workshops is that of keyword research and the behavior of a specific target audience using my all time favorite research tool, Wordtracker.
For those who have not heard of, Wordtracker it is a Web based service that will help you discover which keywords and phrases will be most effective for attracting the right audience to your Web site. Not only that, but the service also tells you how competitive your keywords are (or how many other competing Web pages have been optimized with those keywords in mind) plus how many people have actually searched for those keywords in the past within the last 60 days on the major search engines.
Wordtracker can be used for even more powerful things than just "researching keywords." I'll be revealing much more in the future about the impact of researching "visitor behavior" vs. keywords.