Originally Posted by Rigrunner

Not sure if this has been mentioned on the forums or not but Bruce Clay has a lot of useful tools and tutorials about SEO

Here's one of the free tools pages
http://www.bruceclay.com/web_rank.htm

Google Keyword Tool
https://adwords.google.com/select/KeywordToolExternal

The above link is handy because you can see what people search for, keyword popularity and where the competition is when it comes to buying and using certain words and phrases.