A WordPress plugin which lets you check your ping list. It can be used to verify all domains in the ping list are unique and can also be used to test
The Ping List Checker plugin for WordPress allows blog owners to verify if whether all sites in their ping list are unique or not. If duplicate entries are found, the plugin will report them and will display the number of times they were found in the list. This will help WordPress blog owners to ensure that a ping service is not pinged more than once, and is also very helpful to eliminate double pings which could lead to you getting tagged as a spammer!
Check out some of the other WordPress plugins by the same author.
Just added to version 1.1 has an ping list checker built in that reports if the ping URL connection is alive or dead. However, it requires that "Pear" be installed on your hosting server to work.