In terms of free versions, there are 2 keyword research tools that are the best in my opinion and then a bunch of free tools which will help in varying degrees.

Here are the 2 free tools:

Wordtracker Free Tool
http://affiliate.wordtracker.com/r/699/a/152451/l/v42ax8

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

A nice free brainstorming keyword tool I like to use is:
http://www.kwmap.net

You can also check out my blog where I will be posting more information on Keyword research – my goal is 5 posts a week .

http://www.HowToChooseKeywords.com/

Hope this helps.

Cheers,

Lauralee