Free SEO Research Toolkit - lot of tools

I have a bookmark folder in my browser. I have a collection of links on it. I have named the folder as “SEO Research Toolkit”. It has some SEO and Research related toolkit which I use to create, manage and track my websites and competitors. I just thought that I will put them on my blog so that people can also get benefited from it. I will add some comments from my side

So here is the list:

• Google Adwords Keyword Tool - The most famous and most used tool to find keywords and the number of search for the keyword.
• FREE Wordtracker Keyword Suggestion Tool - I use it with Adwords Keyword suggestion tool and Overture keyword suggestion tool to find more keywords.
• Keyword Ranking Monitor - I use this to monitor rankings for ALL of my sites on Google for various keywords.
• SEOBook Keyword Tool - A great tool to find related keywords and competition on it.
• Search Engine Spider Simulator - I use it to see how search engine spiders see my site. I use this to see whether I am using the right ratio of HTML and text in my page.
• SpyFu - This tool can help you spy on your competition. I use it to see how many advertisers are available for each keyword and how much they are willing to pay.
• Copyscape - I use this tool to verify that nobody is copying my content. Also to verify that the article writers I am using are not copying the content from any other website.
• Google Trends - To find the latest keywords to create websites on.
• Google Zeitgeist - To find recent host topics to create websites on.
• PR Calculator - Quite old but still useful. I use to while building links to get approximate idea of how much links I need to build.
• Domain Pop BackLink Checker - I use it to check my backlinks.
• Dead Link Checker - To verify that there are no dead links on my site. I also regularly check my awstats to find any dead links on my site.
• Top 500 Search Engine Keywords Of The Week - They recently stopped updating it, but it was a good resource to find out what is being hot in this week.
• SEOMoz Page Strength Tool - I use it while buying new websites.
• Keyword Density Checker - I use it to check the keyword density on my web pages to see that I comply

I hope this list if of good use to you. Is there any other tool you use (other than your own site ) then post in the the comments. I would love to add it.