You can use this tool
to perform free keyword analysis on various keywords you are
interested in. It performs keyword market analysis to measure
ones ability to generate traffic from them. You will need
to gather the "monthly searches" and "web page
matches" from the web and input these into the GotSEP
keyword analysis calculator below.
Perhaps the best data on the web is found at Wordtracker. They offer free trials of their service to anybody that has an email address but you can also purchase various lengths of subscription memberships at reasonable prices. If you do use Wordtracker then keep in mind that "monthly searches" roughly corresponds to their "count" multiplied by 30 and our "web page matches" corresponds to their "competing".
You can also piece together data from the Overture search term suggestion tool and search engines like Google. The Overture tool can provide a rough idea of the "monthly searches" by typing in a keyword and seeing how many times it was searched for on Overture and its affiliates during the month indicated. In Google you can perform a search for your "keyword" in quotes and look in the upper right hand corner to see the number of web page matches for that keyword. It is worth noting that this method is not always a true measure of the effectiveness of the keyword since Overture often times groups together search frequency for various keywords. However, it does illustrate the concept behind keyword market analysis.
For an illustrative example of how to this keyword market analysis can be used to bring targeted traffic to you website then please read our article Utilizing GotSEPs Keyword Market Analysis.