One of the best ways to get visitors (prospects) to your site is via search engines. Web users find your site through search engines by entering keywords or key phrases. Nothing beats a site that ranks high on search engines for selected keywords.

However, you should know which keywords net surfers use on search engines. For example, if you have a site that provides Boiler Repairs and sells Boilers for homes and offices in the UK, you should research to know which keywords your prospects might employ.

Through the keyword tools listed on this page you can discover additional, and probably better, keywords based on your selection. Thus, taking our example above, the keyword tools would not only list out keyphrases based on “Boilers” but also synonyms that would help you in understanding visitor search patterns. You can then construct keywords based on those which were listed by the services and develop the web page content accordingly

Part of the Adwords program and free to use.
Google Keyword Tool

WordStream’s keyword management tool for PPC and SEO.
WordStream

Free online keywords suggestion tool that also offers free keywords packages.
Actual Keywords

Find the right keyword for your SEO efforts using the Self SEO keywrod suggestion tool.
Self SEO

SEO Books keyword suggestion tool requires you to register for a free account. You can now generate keywords using their list generator.
SEO Book

Wordtracker’s free keyword tool is one of the industry’s well-recognized services.
Wordtracker

KeywordDiscovery generates keywords from data collected from many search engines.
KeywordDiscovery.com

The keyword tracker from Submit Express shows how many daily searches a keyword gets. Use this tool to research the best keywords for your web site.
Submit Express

Enter a keyword, select the option and search for it. You can also limit the search to a region (country). The service shows the popularity trends for the searched keyword.
SEMRush

Employ the SlowSEO.com keyword selector tool to quickly compare keywords using CPC and KEI.
SlowSEO.com

Know more about your competition with iSpionage.
iSpionage

KeywordEye tool is slightly different from the rest because it shows you (visually) the suggested keywords based on what you queried.
KeywordEye

Simple keyword suggestion tool that provides a detailed list of the most popular search words and phrases.
Addme.com

Find niche keywords using Wordpot.
Wordpot

HitTail offers a keyword tool that supposedly drives more long tail traffic to your site!
HitTail

Webconfs.com’s Keyword Playground (catchy name) shows suggestion an monthly reports based on your query.
Webconfs.com

The services below are not ‘direct’ keyword discovery tools so to say. However, they can help you know which keywords your competition uses and you can then eat their lunch. The Alexa tool provides a decent list of the keywords while Compete, at the time of writing, gives only the top five (you can pay to access more data).

You’ll find the keywords in the ‘Site Info’ section once you enter the address of a web site.
Alexa