The newest keyword research tool available is Google Insights for Search.
This new tool lets you type in a search phrase and graphs out interest over time. While the graph will tell you how many searches have been done for a particular term over time, the numbers aren't absolute search volume numbers, just a gauge of popularity.
You can also see regional interest for a particular term, either targeting a country, or if you choose the United States, you can see search popularity for that term by state. You can even get a breakdown by city.
So how is this helpful? Here's one way to use the tool. If a client wants a paid search campaign, and the campaign lends itself to geotargeting, we can run the advertisements in popular areas to get the biggest impact.
If you advertise locally via paid search, you might also find the search phrases that give you the largest number of impressions in your market.
Of course, the trend graphing feature is impressive. You can learn how many searches occurred for a particular phrase over time, and you can learn about related top searches and searches that are on the rise.