TechCrunch on HitTail:

Bloggers interested in building search traffic should check out New York based HitTail, a deceptively simple tool that makes suggestions for words to use in blog post titles or topics to write about based on the search terms that are already bringing people to your site. It’s based on the theory of the Long Tail, in this case the idea that the most high profile sources of traffic to your site actually make up less than the total sum of all the traffic from small sources combined. What could be more fun than an easy way to look at the long tail of your blog’s search traffic?

I’ve been using it for a month, have yet to see real results since I get some of this info from other WordPress plugins but the recommendations look spot on.