Please tell which is the most powerfull tool in the SEO?

Google Webmaster Tool, Google Analytics and Google Adwords Tool these all three tools are fantastic and very important for SEO.

SEOMoz's suite of products has essentially provided us the value of our own personal SEO consultant. We use their tools track keyword rankings, rate on-page optimization, and track links to our site.

For me it is webmaster tools.

You could also check our SEO/webmaster tools such as A1 Sitemap Generator and A1 Website Analyzer (see links at top of the forum)

I think Google Analytics, Google Adwords Tool and Google Webmaster Tool are the best tool for the SEO.