Firefox Addons

Firefox Addons

• SEO for FireFox - An extension for your browser that changes your Google search results into MIT dissertation. Well maybe not that awesome, but it really does give you a lot of information relevant to why certain sites are showing up in the top 10 results of Google and what kind of competition you'd experience trying to get into those ranks. Also a nice way to find sites that are using the nofollow attribute.
• Greasemonkey - Used by more advanced users who would like to create their own scripts or use other Greasemonkey scripts for SEO purposes.

Other

• Google Analytics - Although this isn't really related to SEO, Google Analytics has a section that displays all the search terms that your visitors used to get to your site.
• Advanced Google Searches - A bunch of advanced Google searches that are done automatically with this nifty little tool.
• Crawl Test - Looks at a given URL to check for any common problems that might prevent your site being crawled properly by a search engine.
• Google Webmaster Tools - A decent collection of tools from Google that also will notify you if your website is being penalized (if you verify yourself as the site owner).
• SEOToolbox - A bunch of random tools from Seomoz.