Google Insights allows you to see trends with search terms, including which regions of the world have the highest incidences of search for specific terms, and also how popular searches are over time.
Google Insights results
(Click for larger image).
Step 1: Visit Google Insights
Step 2: In the box labeled Compare by, select whether you want to compare a number of search terms to see the relative differences, search which locations have the most searches, or view the search history over time.
Step 3: Enter your search term or terms. If you have a single term just enter that term and move on to the next step. If you want to compare multiple keywords or phrases, enter them one by one by clicking the add search term button.
Step 4: This step is optional. You have the ability to narrow the search to a specific country or date range using the drop down menu choices.
Step 5: On the far right hand side of the page, click the Search button.
Step 6: You can now analyze the results in the chart that will appear. At the top is a visual indication of interest in the keyword(s) over the last five years or so. Regional interest is shown using a color code. In this example, Australia has the most searches for the term fitness instructor. Below that, you can discover other keywords that might be useful to you.