Advanced Link Manager – Analyze your website’s link popularity, find link partners and valuable information about them.
Product Page: http://www.advancedlinkmanager.com

Rank Tracker SEO Tool – Rank Tracker is an all-in-one rankings monitoring SEO tool for webmasters and professional SEOs who need to monitor their site’s positions in more than 250 search engines.
Product Page: http://www.link-assistant.com/rank-tracker/

SERank – RAGE SERank will monitor search engine rankings for any number of keywords and display changes in a web site’s search engine rankings over any point of time.
Product Page: http://www.ragesw.com/products/search-engine-rank.html

Advanced Web Ranking – Advanced Web Ranking is a search engine ranking software that emulates a manual search through each search engine. It works exactly like if you were manually checking your keywords ranking position via a browser.
Product Page: http://www.advancedwebranking.com/

Link Assistant – A search engine optimization software program designed to automate the many tedious link building tasks us SEOs need to do on a daily basis. A complete, feature-rich, easy-to-use environment.
Product Page: http://www.link-assistant.com/

iWeb SEO Tool – Quickly and easily optimize your iWeb based website for search engines then publish directly to your iDisk or FTP server without ever leaving the application.
Product Page: http://www.ragesw.com/products/iweb-seo-tool.html

SEO Spyglass – SEO SpyGlass is an extremely powerful competition research tool that is amazingly easy to use. In three simple steps SEO SpyGlass will show you exactly how your competitors got top positions in search engines so you can learn how they do it, improve on it, and get your own site ahead of them, in 232 local and international search engines!
Product Page: http://www.link-assistant.com/seo-spyglass/

WordButler – A wordtracker competitor specifically designed for mac users.
Product Page: http://www.wordbutler.com/

I have compiled some of the free keyword research tools that I have used and currently using for my seo projects. If you can add more, please feel free to leave it in the comment section and if I find it useful, I’ll add it in the list.

1. http://www.keyworddiscovery.com/search.html – This tool generates the top 100 keywords compiled and collected from a total of 181 search engines worldwide
2. http://www.iwebtool.com/keyword_lookup/ – This tool provides list of keywords looked up via the 3 major search engines – Google, Yahoo and MSN. It shows number of searches per day and per month
3. http://www.spyfu.com – This tool is one of the best I have used with its amazing feature wherein you can view stats of adwords for a certain keyword. You’ll get to know number of search results, total advertisers, clicks per day, cost per click and possible cost per day
4. https://adwords.google.com/select/KeywordToolExternal – This tool provides advertiser competition, previous month search volume, and average search volume. It also gives suggestions on related keywords to consider
5. http://www.googleduel.com/original.php – This tool compares competition between two keywords
6. http://www.gorank.com/seotools/ontology/ – This tool provides synonymous terms for a certain keyword entered

There are more free keyword research tools out there, I’ll make an update on this post whenever I see one which is useful. Feel free to add yours too.