What's your favorite keyword tracking tool?

What’s your favorite keyword research tool?

Have you ever used a keyword tracking tool to see what words are being searched? If not than I suggest that you do, it’s valuable info knowing what was searched last month

2 of the top ones I’ve used is the free one in google adwords
https://adwords.google.com/select/KeywordToolExternal

wordtracker is nice, they have a 2 week trial, worth checking out
http://www.wordtracker.com/

What have you used? What did you think of the results?
Discuss