This keyword tool, currently in beta, pulls out keywords on websites aimed at Google Adwords users. However the amount of useful information you can get should make it of interest to anyone who markets their websites. There is a monthly searches column as well as direct links to the landing page per keyword.
One thing that makes this really interesting is the search terms you can find on sites in your niche that you may never have heard of.
Check out the tool here: sktools
