The above said tools gives only approximate results. You can also cross-check your statistics using Google's Insight search, Google Trends etc.

Although they give approximate results they are quite reliable.

Actually I don't think there is any tool that could provide a 100% accuracy. Still google adwords tool could really provide much help.

adwords is a good way to advertise your website, but ,,,,,,you must have enough budget!!
good luck!

Not that accurate as you thought, you know buddy especially when you wanna your rankings everyday.

I think it is a very useful tool.. I read a few articles that say Google may over inflate some of the numbers, but i do not know if that is true or not.
It is a good tool to help you find keyword you haven't thought of too.

adwords is used for ad , and provided by Google to help advertisers determine the best keywords for their sites

As most people here, I think it is not accurate. But is it clearly the best you can get. They have so much more information than anyone else, and a added benefit that noone has mentioned is that you quickly get an overview of the "auto-completion" thingy that google offers when you start to write a keyword in the search bar.

The popular ones will show up as related keywords, and you can then use this information to either go long-tail with your keyword optimization, or to buy cheapish keywords through adwords.

Oh, and another option I forgot about is the excelsheet bing offers. A bit more hassle to set up, but quite helpful

If you target Google for rankings in its result pages then Google Adwards is good for selecting keyword tools.

Yes, and even if you are targeting other search engines. I assume people uses the same keywords even if they are on another machine (even though the auto-complete function might distort this a bit)