Updated 2011-10-06 with Google's new Pagerank URL. Update both your bookmarklet and userscript for the change to take effect.
The currently available solutions have two drawbacks:
To install the bookmarklet (below) simply drag it to your bookmarks or "right-click" on the link and save it as a bookmark (or add to favorites). You can then execute the bookmarklet when visiting a page, by clicking on the bookmark.
The results shown by the bookmarklet, do not look very nice, a page
with PageRank 4 will give us
Rank_1:1:4, while a page without
PageRank is simply blank. The bookmarklet cannot change the
appearance of the result as a script is not allowed to change
pages on other sites for obvious security reasons.
However the Greasemonkey userscript (below) will beautify those responses
and transform it into a standard looking Google PageRank bar.
You'll need to use Firefox with the Greasemonkey addon and if you
do just click on the link below to install the userscript.
These two screenshots show the output of the Google PageRank bookmarklet with and without the PageRank Beautifier userscript:
So there you have it, unlike other PageRank bookmarklets, this bookmarklet does not depend on any third party to work, everything is taken directly from Google's servers and unlike toolbars or addons not all of your activities are logged by Google. Enjoy!
For feedback or bug reports: contact me by E-mail