SeoQuake it's a SEO extension, helps web masters who deal with search engine optimization and internet promotion of web sites. It was available only for Mozilla Firefox, now it's available for Google Chrome too.
Displays the Google PageRank, Alexa rank and other SEO parameters of any webpage, highlights nofollow links, text density, check and compare urls.
Full list of SEO parameters:
Google PageRank
Google Index
Yahoo links
Yahoo linkdomain
Bing index
Alexa Rank
Webarchive age
Delicious index
Whois link
Page source
SEMRush rank
Nofollow links
Click here to Install it
SEO For 2010:Search Engine Optimization Secrets - Kindle Bestseller (Search Engine Optimization Technical Series)