DigPageRank.com: http://digpagerank.com SEOlogs.com: http://www.seologs.com/pr-check/pagerank.html VerifyGooglePageRank.com: http://www.verifygooglepagerank.com
http://checkpagerank.net- here you can also see the link popularity and whether the PR is genuine or not.
There are many PageRank programs on the net.. you might want also make sure that PR is valid for the domain. I use http://www.tracerank.com
My favorite program to use is smartpagerank.com. Because you can also check their backlinks after. If you have the google toolbar installed it should tell the PR also. But you need to make sure it's not a forged PR. Fake PR's are there and sometimes you have to be careful. The best way is to double check against multiple websites.
google it Most of the better known ones have been listed here, but there are many many more out of the net, just google "pagerank checker"