"I've used many keyword tools over the years and Keyword Researcher is up there amongst the most useful of them. Apart from being a great way to get ideas for content, as an AdWords consultant, I also use it to uncover words and phrases that my clients would not want to be bidding on (negative keywords). This is a real time saver for me and a budget enhancer for my clients! All in all, this is a great app and should be used by any professional search engine marketer."
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input. In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).