This the list of useful SEO TOOLs
http://website.grader.com/ - A simple website analyzer with some helpful tips for your site
http://www.allno1.com/google_serp/mu...nk_checker.asp - A nice worldwide SERP checker.
http://www.checkpagerank.net/ - Nice PR checker and validator when exchanging/purchasing links
http://www.iwebtool.com/backlink_checker - Nice but limited way to see what sites link to you and their associated PR's.
http://www.copyscape.com/ - Check to see who is copying your stuff and take action.
https://adwords.google.com/select/Tr...timatorSandbox- Nice traffic estimator. Type in the keywords you want to estimate,maximize your budget and you'll see what Google sees as potentialtraffic. Usually used for Adwords but nice to use for estimating nichemarkets for website development.
http://collinlahay.com/2007/11/16/un...and-gov-links/ - Nice article on link development for any niche.
http://seodigger.com/ - Gives a search estimate for specific keywords to your niche at different SERP standings. Nice.
http://www.ksl-consulting.co.uk/google_penalty.html - Good list of things to be careful about so you don't get a Google penalty.
http://searchenginewatch.com/2175271 - Article on creating an RSS feed for your site.
http://www.diagnosticoweb.com/ - Good all around site tool.
Source : List of Seo Tools