Here is a short list of some of the free research tools available out there. I know it is not comprehensive but these just happen to be a few that we prefer. Enjoy!
Free Keyword Suggestion Tool
Another keyword tool but this one will also give you suggestions. Probably a good cross reference with Google’s keyword tool among others.
http://freekeywords.wordtracker.com/
Keyword Questions
A nifty idea that will show you what people type in the form of a question when it comes to keywords. For example, “how to I change a light bulb” might be a questions for the keyword phrase “light bulb”.
Google Alerts
Stay on top of the competition, your market and what people are saying about your company with Google Alerts. These are sent directly to your inbox as they happen and are a great way to stay in the know. A personal favorite.
http://www.google.com/alerts
Google Trends
A tool that shows you what is the most popular topic in nearly real time. You can also search certain trends and it will give you an awesome chart and all sorts of fun facts in relation to how trendy your search phrase is like what city it is most popular in.
http://www.google.com/trends
Google’s Keyword Tool
A keyword research tool that shows you some cool things like how popular a word or phrase is, how competitive it is, what month it is most frequently searched for and a whole lot more.
https://adwords.google.com/select/KeywordToolExternal
Google Insights
This little tool can help your marketing efforts by showing you charts and other information about what people think is most important and you can search by regions.
http://www.google.com/insights/search/#
Yahoo! Site Explorer
See who is linking to your site or your competitors site by simply entering the domain name in the search box. This also shows you what pages are indexed by the Yahoo! Search engine.
http://www.google.com/alerts
SEO Quake
SEO Quake is a Firefox plugin that can help you research keywords, meta tags, inlinks and more right from your browser. This is a must for SEOers.
http://www.seoquake.com/
Rank Checker
Rank Checker is a great tool that will show you where you rank in the top 3 search engines for whatever search strings you input. This is great for tracking your SEO progress and see where you stand amongst the competition. This is free but you have to sign up for the SEO book emailer. Worth it.
http://www.seoquake.com/