The Google External Keyword Tool will help business owners understand how their audience searches for them. And it will help you utilitze negative kewords - for example eliminating those who are searching for a free vacation, you're not interested in people conducting those kinds of searches.
While I normally tell my session participants to have an expert run their keyword campaigns and SEO (search engine optimization) there are a few of you who handle it yourselves.
I've only taken a passing glance at the tool but like all Google tools, it's easy to use, free and has lots of help features.
Like I preach in my sessions - repetitive content is key to natural search engine ranking, and this tool can help you find your meta data keywords and your content keywords.
So if you're stuck on keywords, give this tool a try.