W3C Markup Validation Service - This is the W3C Markup Validation Service, a free service that checks Web documents in formats like HTML and XHTML for conformance to W3C Recommendations and other standards.

Watchfire - This is a free online service that lets you test single pages of web content for quality, accessibility, and privacy issues.

Web archive - Browse through 55 billion web pages archived from 1996 to a few months ago.

Web Page Analyser - This tool will read the page you specify, and put it through a few basic tests to see if qualifies as "search-engine-friendly" for the phrase you specify. It then gives a report on the good, and the bad points of the page in SEO terms.

Web Page Screen Resolution Simulator - This tool will simulate your web page in different screen resolutions.

Website Keyword Suggestions - This tools tries to determine the theme of your website and provides keyword suggestions along with keyword traffic estimates.

Website to Country - This tools helps determine the Country in which the specified website is Hosted.

Whois Source - This tool supports many types of searches: IP address searching, invent a new domain with our domain suggestions, partial word(s) searching on active domain names, domains for sale, domains at auction, full domain.

WordTracker - This tool will help you target the right keywords for better search engine placement.