This plugin censors any IP and/or URL.
/noadsreload noads.noadsreload
/noadstest noads.noadstest
/noadsurl noads.noadsurl
http://dev.bukkit.org/bukkit-plugins/noads/pages/blacklist/
http://dev.bukkit.org/bukkit-plugins/noads/pages/blacklist-how-to/
All you do is add stuff to the blacklist.txt