What are the best ways to find keywords that will convert for any given niche? I realize testing is an obvious answer. I bring up this question because I've seen ads for products that will allow you to "steal your competitors best converting keywords." Any ideas on how to do this without buying another over-hyped ebook?
Google Analytics is a good tool if you have access to it and are using your own site. That way you can see which keywords convert automatically through non CPC methods.
SpyFu is another popular tool. They allow you to view some information for free but full access will cost you. I have found the free tool quite useful in the past. http://www.spyfu.com/ Good Luck
the best converting keywords are always KEYWORD + CALL TO ACTION example buy widget get a widget signup for widgets if the searcher is using a call to action then they are in the very last buying phase and highly convertible
You can try keywordspy. Don't rely on it exclusively though. It can however give you good insight as to what your competition is doing.
Use both the Google Keyword Tool and the Google Keyword Traffic Estimator. Combine them and use some good SEO on your site plus a lot and lot and lot of link building in a slow and constant phase to pages that target your keywords.