I use Ultimate Niche Finder now. In the past I used market samurai, keyword scout, and google adwords.
The reason why I like UNF is because it's really easy to use and you can spot the easy keywords to rank really fast. There is BHW member who's selling it here, search for it and you'll see it. I use both UNF and google adwords now. What I do is use google adword first to generate some keywords from main keywords. Copy them into UNF, and try to expand all the keywords even futher. Select all and click analayze, in which it gives color code of which one are easy to rank. Green = Easy, Light Green = Easiest, something like that, can't remember off my head. Filter all the easiest and easy and your good to go.
Market Samurai, just doesn't work anymore for me, and really just gave up trying. Keyword Scout, well that was dam waste. Keyword Scout always asked for my registration information, and thus got fed up and just don't use it anymore.