Keyword research is the process of identifying the keyword phrases that your potential customers type into search engines to find information about your products and services.  The goal is to identify the most popular and relevant keywords that you can target for search engine optimization and paid search.

There are many keyword research tools out there, but none of them are perfect.  In fact, if you test the same keyword phrase in each of the top keyword research tools, they will return drastically different search volume estimates.  So when you use these tools, you should understand that the goal is not to estimate the precise number of annual or monthly searches – the goal is to identify which keywords phrases are more popular than others. 

Imagine you sell widgets and keyword research shows you that people search more for blue widgets more than red widgets.  You may decide that you should optimize your website for blue widgets rather than red widgets (search volume may be too low to justify the effort)  or widgets (search volume may be too high and too competitive to get traction in the top search engines).

Here is list of the most popular tools:

Keyword Discovery – Offered by Trellian, this tool compiles annual keyword search statistics from over 180 search engines, to create one of the better tools out there.  Unfortunately, the top three search engines (Google, Yahoo and MSN) are not included in this estimate, so the tool is still not perfect.  There is a small monthly fee to use this service.

Wordtracker – A keyword analysis tool designed to help one determine which keyword phrases to use in their search engine ranking strategy. This valuable tool can tell how often people search for a specific term and how many competing sites use that same term on search engines.

Google AdWords Keyword Tool – Get ideas for new keywords that can help you improve your Google AdWords relevance. If you’re running your ads on broad-matched keywords, this tool may help you find additional keywords.

Overture Term Suggestions Tool – This tool shows how many monthly searches are performed each month in Yahoo.  It works sporadically lately.