Firefox Add-ons

• The Firefox Browser
• Web Developer - Adds a menu and a toolbar with various web developer tools.
• Firebug - CSS/JS development tool - Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page...
• Yslow - YSlow analyzes web pages and tells you why they're slow based on Yahoo's rules for high performance web sites.
• Sitepoint reference tool - The SitePoint Reference Tool is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
• SeoQuake - Seoquake is a Mozilla Firefox extension aimed primarily at helping web masters who deal with search engine optimization and internet promotion of web sites. Seoquake allows to obtain and investigate many important SEO parameters of the internet...
• SEO for Firefox - Want to know why Google or Yahoo! ranks pages? If so this is the Firefox extension for you. SEO for Firefox pulls in many useful marketing data points to make it easy get a holistic view of the competitive landscape of a market directly in the search results.

Mixed list of Very Useful Tools:

• Google Webmasters Tools - A collection of Google Tools to help webmasters
• Google Analytics - Great and FREE analytics tool (what are visitors doing on your site?)
• crazyegg.com - Supplement Google Analytics with stunning visual representations
• Xenu - FREE and very good windows based link checker
• Ranking Manager - A great (and essential!) keyword ranking tool. ($150 well spent!)
• PangeRankBot - What is the pagerank of each page on your site?
• OptiSpider - Tool to help you optimize your internal site linking strategy.

Keyword Suggestion and Valuation Tools

• Wordtracker Free Keywords - free keyword suggestions from Wordtracker. Wordtracker also has a more advanced paid version, and sells top keyword reports.
• Google AdWords Keyword Suggestion Tool - recommends keywords based on a keyword you enter or a URL you have the tool analyze
• Google Traffic Estimator - shows the estimated bids prices and ad clicks for the top ranked AdWords ad. Allows you to check for [exact match], "phrase match", or broad match.
• Google Search Based Keyword Tool - shows keyword search volume estimates and keyword values...by keyword, site, or category.
• Google Suggest Tool - shows frequently search for phrases starting with the words and letters in your query.
• Quintura - Find keyword associations and refinements.
• Keyword Discovery - free keyword tool from Trellian. Trellian also has a more advanced paid version of Keyword Discovery.
• Microsoft Keyword Forecast - shows predicted Microsoft search impression count and historical trends.
• Wordze - nice for generating decently large keyword lists quickly and inserting them into paid search campaigns.
• Yahoo! Search Marketing - Yahoo! has a keyword research tool inside their platform. It is really bad marketing of them to only have the new tool accessible inside their platform, while neglecting their old keyword tool.
• SEO Book Keyword Suggestion Tool - tool shows top keyword phrases from Wordtracker.
• SEO Book Keyword tools - Additional useful keyword suggestion tools.
• Spyfu.com - Research your competitor's keywords.

Many more tools from the SEObook website:

1. Search Analytics Tools - establish your marketing goals and establish a baseline for where you are at right now.
2. Keyword Research Tools - discover the keywords your customers are searching for right now.
3. Competitive Research Tools - see what keywords your competitors are targeting.
4. PPC Tools - buy important keywords and track the results to understand how well they convert,which helps you focus you organic SEO strategy on the most profitable keywords. Save money using these free Yahoo! Search Marketing & Microsoft adCenter Coupons.
5. Link Analysis Tools - start building your link profile and track your progress compared to competing websites.
6. Search Engine Ranking Checkers - determine how effective your marketing is by watching your search engine rankings improve.