Wordtracker, long known for their keyword suggestion tool, has another interesting tool worth some attention, for SEO benefits, PPC and even suggestions for new content. Keyword Questions will show you what questions users are asking about your chosen keyword. The results show a "times asked" figure that represents how many times that question has been asked "... on our partner search engines in the US," over the course of the last 140 days. This information can be useful in a few different ways.
SEO: Like Wordtracker, you can identify terms and keywords that are being used while typing questions into a search engine. For example, enter "coffee" and you'll see that people are asking about coffee makers, iced coffee, coffee mugs, coffee pots, caffeine, coffee liqueur, etc.
PPC: Aside from the obvious targeting benefits of this information, you can also get some good "negative" keyword analysis. In other words you can find some terms that you want to use as qualifiers, so that you're not paying for unqualified clicks. Read more about negative keywords.
Content: This is perhaps one of the better uses of this tool. After entering your keyword, look at the questions being asked for great content ideas for your blog, or even new pages of your site. Returning to the coffee example, you can see that it would be a good idea to write some content about coffee origins, different ways to brew coffee, or ways to clean coffee pots and coffee makers. There's also a reference to "clouds in my coffee," which apparently are lyrics from a Carly Simon song. Perhaps a running forum on coffee in popular culture?
Another good tool is Yahoo! Answers. You can search terms, and see related questions and user answers. There, "coffee" returned 94,972 results.