Long Tail Pro by Spencer Haws is the most useful keyword research tool that you can use for your internet marketing. Thousands of webmasters depend on the tool to generate thousands of keywords. It is such effective that it has dominated the keyword search market for the few years it has been into existence. It would cost you less than one hundred dollars to have access to this important life-changing tool.
It's not always about getting visitors to your site, but about getting the right kind of visitors. The usefulness of this intelligence cannot be overstated; with keyword research you can predict shifts in demand, respond to changing market conditions, and produce the products, services, and content that web searchers are actively seeking. In the history of marketing, there has never been such a low barrier to entry in understanding the motivations of consumers in virtually any niche.
Note: the old software version of Long Tail Pro would have spit out several hundred adwords suggestions (many being irrelevant to the seed keyword) for this one seed keyword and then you would have to filter to see only what you wanted to see. With the new cloud version of Long Tail Pro, you set it to show only a certain number of keywords and it displays the most relevant keywords so you have less noise and confusion to filter through.

It would be great if you can provide comparative analysis of this tool with Google Keyword Planner. Since you’re using this tool so you can provide best comparison. One differentiation which I understood is that this tool works for yahoo and bing as well whereas Google keyword planner works only for Google but Google being a dominating search engine, gives the highest returns, so only this reason may not be enough to buy it.