Here’s a list of tools which I find useful and available for FREE:

1. Test Everything - Like the name implies, this is REALLY a tool that test everything for you. There’s actually more than 100+ tools via this link. One word of warning though, sometimes this webpage can take a very long time to access, probably due to traffic load.

2. SEOmoz Page Strength Tool -The tool is designed to satisfy the curiosity of webmasters, surfers and web marketing professionals seeking a better metric to quickly assess a site/page’s relative importance and visibility Here’s the benefit of using this tool : To check the Relative Importance and Visibility of a Webpage, The Potential Strength and Ability of a Page to Rank in the Search Engines, Data on Popularity and Links & Mentions of the Page Across the Web.

3. iwebTool - I love this website because there are several wonderful tools that I frequently used. Among them, my favourite is Google Page Rank Prediction but I must admit that it is not very accurate. I simply use it to gauge whether my blog PR is going up or down when there’s rumours of Page Rank updates.

4. Backlinkwatch - This tool provides complete detailed information about quality and quantity of backlinks pointing to your website.It will show you “anchor” text, pagerank, total outbound links on that page, and nofollow flag for each of your inbound link available.

I’m not very SEO, so I do not really use SEO tools except the few listed above and I don’t even really analyze the result. However, it is really very easy to find more such tools if you are interested. Just do a google search for SEO tools and you’ll find plenty.