I have just read that Google appear to be pulling their external keyword tool from circulation soon.

See: https://support.google.com/adwords/bin/answer.py?hl=en&answer=2511914

This is a vital tool for the research  behind search engine optimisation. Google tell us to produce good content then they won’t tell us how.

In future you will need an AdWords account to access this information. So the slow slide of Google into ‘evil’ (their moto is ‘do no evil’) continues. They take the search information we give them, which they sell to advertisers and slowly they give us back less and less…

I recommend you research your keywords whilst this information is still freely available. Other systems exist for keyword research, but I’ve always found the quality of their data to be dubious.