A question that often comes up from people looking into search marketing involves the source of popularity data that many keyword research tools report. Below are notes on several of the most often used tools, paid and free. This is not comprehensive by any means, but very helpful for quick checking.

Wordtracker.com gets keyword data from Dogpile and Metacrawler which are a combination or collection of search results from various search engines.

Other web based tools like KeywordDiscovery.com get their information from ISPs that share aggregated Internet usage data of their users.

Overture's free keyword suggestion tool inventory.overture.com shows the estimated number of searches performed in a 30 day period.

Google has a similar tool but it does not report any scores or search frequency numbers adwords.google.com/select/KeywordSandbox (at least not yet)

SitePoint has a handy tool that compares Overture and Wordtracker keyword results side by side.

Another useful tool for keyword suggestions is Google Suggest.

Tags: keyword research, optimization, keyword tools