Today I’ve searched for a plug-in to see a site’s google ranking. I’ve found severals. They are all pretty good. My advise is not to install all of them in the same time.

SEO Quake
In the search engine query, this add-on tells you the Google Page Rank, number of indexed pages within a website, and the number of links pointing to the page. It also has an option tool bar that goes a little bit more in detail with Yahoo page rank results as well. It is very complete but also very havy (visualy).

Alexa Sparky
This is the best , in my opinion. Highly rated, it shows up on your status bar. It provides SEO information including popularity, Reach and Rank, and related links for each page.

Google Preview
This is another add-on that lists popularity ranks of web sites into the Google and Yahoo search results pages. However, it comes with a significant bonus feature. Search results in Google come with a thumbnail preview of websites. I find this visual reference a real timesaver –especially when I’m looking for a website that I’ve already visited but don’t remember the domain.