SitezMeter

This handy SEO tool shows you the Google PageRank of webpages beside the address box.
The PageRank value is cached locally, so it doesn't have to hit the server every time you switch tab.
Moreover, click the icon in the popup window provides extensive information about web sites traffic - instantly find out how popular a web site is, its rank, and how fast it is growing. Please check out the screen shot for more detail.