In Sep 2009, Google introduced "updated Keyword Tool" beta, which brought increased functionality and streamlined way to identify new keywords for AdWords account. Google now announced that they've "completed the final transition of "Keyword and Search-based Keyword" Tool into the updated Keyword Tool. Both of these tools will be available in their current forms through the end of August, after which time their addresses will redirect to updated Keyword Tool," said Google.
If you haven't yet, give it a try to take advantage of its new look & features. You can always access the tool without signing in to AdWords. However, for best results, you should access it from within your account. Just click "Keyword Tool" link from the Opportunities tab.
Full Set Of Directions: AdWords Help Center