Quarkbase is a free tool that offers an organized and detailed overview of any web site complete with summary, popularity, ownership, traffic information and huge variety of information of any website. A very useful tool.

Knowing who links to your site and increasing the number of quality links is an important part of any web site promotion effort. This free service allows you to query Google, Yahoo, and MSN and reports on link popularity. Most of the major search engines now factor Link Popularity into their relevancy algorithms. As a result, increasing the number of quality, relevant sites which link to your site can actually improve your search engine rankings. There is still no one "secret trick" to getting good rankings, but boosting your site's popularity may give it the edge it needs.

Grade Your Website - Website Grader is a free seo tool that measures the marketing effectiveness of a website. It provides a score that incorporates things like website traffic, SEO, social popularity and other technical factors. It also provides some basic advice on how the website can be improved from a marketing perspective.

SEOmeter.com offers a convenient online SEO tool that allows webmasters to monitor their website's search engine visits and crawling activities, and to collate crawling trend against their ongoing marketing campaign and other SEO strategies.

See your website like a Search Engine sees it.

Find out how well your site is doing in popular search engines, social bookmarking and other site statistics. Check PageRank, Backlinks, Indexed Pages, Rankings and more

Trend Report will allow you to view vital search engine information about any url that you enter. The Trend Report will allow you to see the Urls link popularity, PageRank™, Alexa Rank, keywords that you can find the site by and more.

Checks all the site stats like pages indexed on Google, backlinks and everything you coould think of on SEO basics.

Checks all your internal pages for their Page Rank. Good to determine your internal link structure.

Tests all links site wide and reports any broken links. The spider splits links in two categories, internal, from the same host, and external, outgoing link to different domains. Once you have put your start URL the bot will visit your website and follow all links checking for their status. When finish you will see a report showing all the bad links found, not only 404 status.

Simply type a seed keyword in the below field and have KeywordDiscovery generate the top 100 keywords for you.

Link popularity check is one of the best ways to quantifiably and independently measure your website's online awareness and overall visibility. Simply put, link popularity refers to the total number of links or "votes" that a search engine has found for your website. Marketleap has designed this link popularity tool to help website owners find out who is linking to their site, but also to give a useful benchmarking report to quickly show where you stand in comparison to competitors and other major online players.

The SEO Design Analyzer is a free tool from Raven SEO Tools that can help you build better search engine optimized Web designs. Enter the full address of the Web page you want analyzed, and then click on the Analyze button to receive your free Web design report.

Browsershots makes screenshots of your web design in different browsers. It is a free open-source online service created by Johann C. Rocholl. When you submit your web address, it will be added to the job queue. A number of distributed computers will open your website in their browser. Then they will make screenshots and upload them to the central server here.

This tool will output sites linking in and will list each of the links PageRank. You can also list out the links that have a nofollow attribute.

This fast and accurate keyword density analyzer is 100% free.

* Create an XML sitemap that can be submitted to Google, Yahoo and other search engines to help them crawl your website better. * Create a Text sitemap to have a plain list of all your pages. * Create a ROR sitemap, which is an independant XML format for any search engine. * Generate an HTML site map to allow human visitors to easily navigate on your site.

This tools searches for websites of the theme you specify that contain keyphrases like "Add link", "Add site", "Add URL", "Add URL", "Submit URL", "Add Article" etc. Most of the results could be quality potential backlinks. A backlink could be considered as a Quality Backlink if 1. The Theme of the backlinking website is the same as your website. 2. It links to your website with the keyword (keyphrase) that you are trying to optimize for.

Search Engines are known to act upon websites that contain Duplicate / Similar content. Your content could be similar to other websites on the Internet, or pages from within your own website could be similar to each other (usually the case with dynamic product catalog pages). This tool allows you to determine the percentage of similarity between two pages. The exact percentage of similarity after with a search engine may penalize you is not known, it varies from search engine to search engine, Your aim should be to keep your page similarity as LOW as possible.

This tool will generate a report showing how many pages of your website has been indexed by the search engines so far. It supports all major search engines: Google, Yahoo, MSN, Alltheweb, Hotbot and AltaVista.

Discover competitors' sites with common Google keywords * Get list of Google keywords for any site * Get list of AdWords keywords for any site * Check your competitors landing-pages for SE and AdWords traffic * Investigate long-tail keywords for any domain * Get estimated SE and AdWords traffic for any domain * See sites' spending for AdWords * Get hidden related (and low-cost) keywords to optimize your AdWords campaign * Find potential advertisers for any site * Find potential traffic sellers for your site.

SpyFu lets you see which keywords your competitors are buying and which ones they optimize their site for. Once you understand the competition, you can beat them at their own game or your can exploit their weaknesses.