There is a google tool for advertisers that helps you find the highest rated keywords. Login as for AdWords and try different words. However, I don't know if the best idea is to target the highest rated or the keywords that will match your domain of interest. For example, I blog about Dracula on [url]http://dracula-transylvania.blogspot.com/[/url] because I'm interested in history (medieval history mainly)
all best,
Radu