This is another plugin by SEO Book. The info it provides is very similar to what SEO for Firefox gives you, but it’s presented in a form of an additional toolbar.
This means that it doesn’t analyze a set of sites, but it gives a more in-depth look into the site you’re currently browsing. And the data is shown in an easily digestible form, which can really speed up your research.
Among other info, you get: Google PageRank, number of backlinks, number of directory links, site age, monthly views (by Compete), estimated traffic value.