SEO Chat is another important resource for SEO professionals and webmasters from all over the world. It not only contains articles and discussions, there are plenty of useful webmaster tools which are failry accurate.

It is hard to find another website where you can use a comprehensive array of useful tools completely free. No wonder this site is so popular!

Seomoz.org is a search engine optimization company whose website offers useful tools for webmasters.

Their Page strength tool is quite good (eventhough not quite accurate) to get an idea about a website or a domain. They also have many other useful tools which webmasters will find handy.