Have you seen Google’s Wonder Wheel? You’ll see it as an option on the left side column adjacent to any search result. This nifty little SEO, and I think SEM, map tool allows you to see related search terms that people are actually using. While not data heavy, it does provide a glimpse into optimizing your content for a keyword family. While the SEO implications are obvious, I think this also has applications in SEM. In any case, it is a very visual way to organize the keywords you need to be using on your website, I recommend you check it out.
If you want to learn how to find and use the Google Wonder Wheel, check out this video I found.