Google just released this great little tool called "Wonder Wheel". It allows you to refine your search and find derivatives of keywords. Wonder Wheel is one of a series of refining options that Google has released. The way you use it is by putting in a keyword (broad) in the query box. For the sake of this example I'll use "Bows". When Google sends you back results for your query go up to the top left hand side of the page click on "Show options". This will take you to another page that will allow you to refine that search. Click the link "Wonder Wheel" and a keyword cloud should appear. So, if I'm wanting to put together a website that sells bows this might be a good place to start when thinking about the information architecture of the site and the important content needed for that site. SEO guys and gals should love this app. It's much like the Adwords keyword tool but it's a really great way to research on the fly.
Take a look and give it a whirl!