I would go with Market Samurai, you can't be wrong with that. I think Keyword Elite 2 is great as well but it seems it is focusing more on PPC vs MS on SEO. Perhaps you can still get the original MS for USD97 but I forgot how to do that. Google a bit to find out. I think it was also mentioned here at BHW
You can go with free tools like Google extended Keyword tool, but Commercial Programs like MS or Keyword Elite 2 provide additional very useful modules.