Phil,
I agree, WordTracker has been an industry standard for years. Additionally, I encourage PPC marketers to leverage the Adwords keyword suggestion tool - in my opinion it is the best free keyword tool available.
Also, I recently wrote a "how to" explaining the keyword research benefits of both Google Squared and Google Sets. You might be surprised to see how effective both of these tools are in helping build a "wider" keyword list as well.
Tony
Clickable SEM Guru
Posted on
07/17/09 at 11:14 AM