Jonathan Zittrain and Ben Edelman at Harvard have a site listing URLs that are blocked in China. In addition to some obvious sites (related to things like Chinese dissidents, the Taiwanese government, and Falun Gong), there are some curious sites on the block list, including the U.S. Federal Court system (uscourts.gov).
You can go to their site and try out any URL you like, to see if it is blocked in China.
