I just purchased an amazing keyword research tool that does deep research into the search engines beyond what you can get from the Adwords keyword selector tool. It's no longer on the market (limited time ***er).
To recoup my investment, I am selling keyword lists for $5 each or 3 for $10 (paypal).
As an example of how powerful this list can be, I did a keyword list in the weight loss niche with over 5k results for weight loss keywords. Not every niche will be so search-rich, but you will get far more results than with any free tools out there.
If you want to get long-tail keywords and hidden keywords that your competitors probably won't know about, send me a pm and we'll get you the lists.