In the arena of SEO (search engine optimization) page ranks matters a lot.Valuation of websites depend on its highest Google pagerank and lowest Alexa ranks.
For example
If a site have PR4 one text link cost $7-20 / month depends on the (quality of the content)
You know some time a high traffic websites have a low value of google page rank and high alexa rank due to improper SEO and tricks.

Here i have few tools for firefox like Alexa Sparky and SearchStatus

One way Sparky is a Firefox browser addon by Alexa, that accompanies you as you surf, providing useful information about the sites you visit without interrupting your Web browsing.
Secondly bo the Sparky and SearchStatus contribute to our websites Alexa ranking but later addon comes with extra feature of google page rank also.So SearchStatus is recommended.
So don’t be late to
Download Sparky
Download SearchStatus
If you have more queries regarding alexa ranks and google page ranks then please feel free to discuss here.