I normally use google webmaster tool or yahoo site explorer to download all my indexed pages and then use digixmas's bulkpage rank checker. I guess this is one of the best methods. If you are just interested in finding out PR pages in your website you can use the internal PR checker from seotoolbag.com or use seoquake plug-in for firefox
tools are not always showing right information if you want to check your sites PR then there are ultimate solution that check manually through google tool bar