Have your heard of Google Insights for Search?
This is a powerful keyword tools that allows you to not only perform in depth keyword research, but also allows you to dig down into graphical representation of trends over time.
The tool also has a great mapping element that can show you search trend movements throughout the world.
Below is a video that illustrates Google Insights for Search:
Some footnotes to Google Insight to Search are added by Google themselves:
“This prediction model doesn’t take into account the context of the search term or its category, nor does it account for any business cycles that may be driving a specific market,” says Google in the Insights for Search Help Center. “Please treat these forecasts as estimates only, and not as exact predictions of future values.”
“Looking at search trends helps you understand when, where and how the world’s interests have changed. Simply type in search terms to see how search query volume has evolved over time, in which geographic regions search interest is greatest and other related searches,” Google says.