Well since this questions keeps on popping up over and over again on daily basis on DP, after an effort of 4 hours, I have compiled the Best List of Keyword Research Tools. Cheers and Enjoy
Guys, if you know few more or have something to say about the tools in the list which you have used, please put them as comments since I myself have not used couple of paid tools in the list.
Market samurai is paid tool but available for free 40 Day Beta test. It analyze Keyword Traffic, targeted keywords and much more in depth.
I say being a neurosurgeon is also a no brainer - just spend 8 years learning and 10 more years practising