Free Keyword Resources for Niche or Product Research

Some free resources I use when doing niche or product research are:

http://freekeywords.wordtracker.com
http://www.freekeywords.wordtracker.com/gtrends
http://www.goodkeywords.com
http://www.spyfu.com/

Here are some paid resources that go into much more detail when looking for keywords to help me locate a niche:

http://www.nichebot.com
http://www.wordtracker.com
http://www.keywordelite.com