Besides Google Adwords: Keyword Tool, Are There Better Ones?

Do you use other keyword research tools than Google's Keyword Tool?

If yes, how are they better?

 

Well, I do use others, but I mostly rely on that one, it seems that it's the most accurate one. I use Wordtracker, Word Stream, Trellian and Nichebot as well, but to a limited extent. It would be most useful if someone would suggest some other free keyword tools that are proven to be good. Thanks!