Google toolbar is very good and i am also using freeprchecker.com to get accurate PR result. It's a matter of taste and what is working for you.
I too use a Firefox add-on. (Google toolbar takes up too much room for me.) Also, there is UrlTrends PageRank Commonality which check several (all?) Google datacenters at once. (Capcha is a bit of a pain though.) And finally, I use PaRaMeter to check several sites at once. John
Firefox addon - SeoQuake to check the PR https://addons.mozilla.org/en-US/firefox/addon/3036 Code (markup):
I use the SeoToolbar "SEO Quake" for firefox only. https://addons.mozilla.org/en-US/firefox/addon/3036 Its reliable and gives you some further input like: links, alexa, age etc. Helpull for analysing competition as well.
I use searchstatus and it has worked pretty well for me so far. Had SEO Quake installed for awhile but i noticed it was slowing down my browser when I would do a Google search so I uninstalled it.