Word Tracker
Wordtracker helps website owners and search engine marketers identify keywords and phrases that are relevant to their or their client's business and most likely to be used as queries by search engine visitors.
http://www.wordtracker.com/

Key Word Discovery
Keyword Discovery can tell you the search phrases people use to find products and services, as well as the search terms that drive traffic to your competitors.
http://www.keyworddiscovery.com/

Spy Fu
Spy on your online competitors. Download competitors keywords and adwords.
http://www.spyfu.com/

SEO Digger
SEOdigger is an interesting tool where you can enter your domain (or competitor’s) and find out which of your keywords rank high enough to be listed within Google’s top.
http://seodigger.com/

Keyword Forecast
This tool forecasts the impression count and predicts demographic distributions of keywords. Enter keywords separated by semi-colons and click the submit button.
http://adlab.microsoft.com/Keyword-Forecast/default.aspx

AD Gooroo
AdGooroo keyword tracking tools help you find competitors' keywords, identify the best ad copy, benchmark against other advertisers, find and fix common PPC problems.
http://www.adgooroo.com/

Self SEO
Choosing the right keywords is critical for a success of a website. Target the wrong keywords and you have lost. There is pure gold hidden in less competitive keyword combinations and variations.
http://www.selfseo.com/keyword_suggestion_tool.php

Five Steps to Effective Keyword Research
There's no getting around it. Keyword research is a vitally important aspect of your search engine optimization campaign. If your site is targeting the wrong keywords, the search engines and your customers may never find you, resulting in lost dollars and meaningless rankings. By targeting the wrong keywords, you not only put valuable advertising dollars at risk, you are also throwing away all the time and energy you put into getting your site to rank for those terms to begin with. If you want to stay competitive, you can't afford to do that.
http://www.searchengineguide.com/lisa-barone/five-steps-to-effective-keywor.php