Google recently announced it’s new tool “Search-based Keyword Tool”. Tool generates keyword and landing page ideas highly relevant and specific to your website. In doing so, the tool helps you identify additional advertising opportunities that aren't currently being used in your AdWords ad campaigns.
Based on your URLs, the Search-based Keyword Tool displays a list of relevant user queries that have occurred on Google.com (and on other Google search properties, such as google.co.uk) with some frequency over the past year; these suggestions can be found under the Keywords tab, in the New keywords related to (site) section. In the Keywords related to your search section, you can see a broad list of keyword ideas that are also relevant, but aren't necessarily based on your site.
The keywords are also organized by category. Click any category to expand and view its subcategories. If applicable, you'll also see the keywords organized by brand names.
With this new tool you can get a better sense of what your potential customers are searching for and which keywords you should advertise on.
The tool is also useful if you don't currently advertise on AdWords. For example, a shoe store could discover which footwear styles users are searching for, or a digital camera blog could decide which cameras to review by looking at which camera models attract the most queries.
The Search-based Keyword Tool is now available to all advertisers in the US and UK. Tool will be available in additional languages and more countries in the near future.
More details can be found at: http://www.google.com/support/sktool/