Based on a set of user data accidentally released by AOL from a 3 month period, collected from March 2006 through May 2006, I have created this Keyword Suggestion Tool.
Enter in a keyphrase to see an estimate of how much traffic that phrase would have generated in that time frame for a one month period across the 3 big search engines. You can read more here for an explanation of where the estimates come from.
Clicking on the number under the Google column opens up Google Trends for that phrase for the month of May 2006,
and clicking on the result under the
Yahoo column will bring up the Overture Keyword suggestion tool for the most recent month that data is available.
UPDATE 2008-07-15: Since the Overture Keyword suggestion tool had been finally removed altogether, I have removed the links to that resource from the results table.