Google Keyword Sandbox:

(Not the same thing as the SEO phenomena some people call the Google
Sandbox.)

The Google Keyword Sandbox (http://www.adwords.google.com/select/main) will
show you what terms will be used for AdWords broad matching. In addition it will
suggest other keywords you may want to advertise for. Unlike many of the other
keyword suggestion tools the Google Keyword Sandbox does not offer search
frequency. To test search frequency you need to set up a bidding account for the
specified term (please note: this can be expensive if you do not target your
keywords and / or bid too high).

When setting up a new AdWords campaign, after you enter a few keywords Google
offers showing you related terms you may want to advertise on.

In December of 2004 Google also created a search term suggestion tool by the
name of Google Suggest which auto-completes partial search queries. It does not
show search volumes, but search volume is believed to play a heavy role in its
output. The tool is currently only available in some languages. Many Google
Toolbar installs have this feature enabled.