Go with Google Adwords Keywords Tool............... It is best, reliable, accurate and free.........................
Agree with this... however, if you have some money you can actually buy keywords with the bids so that u rank better
Just google 'external keyword tool' and go to town. With all the new options, I think its better than a paid subscription to wordtracker.
Try market samauri, i started using it recently. Its a lil pricy at $120 but they give you a free trial for a couple days and they got really good tutorials. Really sped up my keyword research.
There really isn't any legitimate good tool out there. Best is too google that keyword and see what your competition is.
I tried a lot of different keyword tools. And I came to the conclusion that most of them are notreliable and accurate. Use the Google Keyword Tool, that is the best one if you want to use Google as you main search engine.