Originally Posted by uno

http://rpc.pingomatic.com/
http://api.moreover.com/ping
http://api.moreover.com/RPC2
http://api.my.yahoo.com/RPC2
http://api.my.yahoo.com/rss/ping
http://bblog.com/ping.php
http://bitacoras.net/ping
http://blog.goo.ne.jp/XMLRPC
http://blogbot.dk/io/xml-rpc.php
http://blogdb.jp/xmlrpc
http://blogmatcher.com/u.php
http://bulkfeeds.net/rpc
http://coreblog.org/ping/
http://ping.bitacoras.com/
http://ping.bloggers.jp/rpc/
http://ping.cocolog-nifty.com/xmlrpc
http://ping.rootblog.com/rpc.php
http://ping.weblogs.se/
http://rcs.datashed.net/RPC2
http://thingamablog.sourceforge.net/ping.php
http://topicexchange.com/RPC2
http://www.a2b.cc/setloc/bp.a2b
http://www.bitacoles.net/ping.php
http://www.blogpeople.net/servlet/weblogUpdates
http://www.blogroots.com/tb_populi.blog?id=1
http://www.blogsnow.com/ping
http://www.lasermemory.com/lsrpc/
http://www.mod-pubsub.org/kn_apps/blogchatter/ping.php
http://www.newsisfree.com/xmlrpctest.php
http://www.popdex.com/addsite.php
http://www.snipsnap.org/RPC2
http://www.weblogues.com/RPC/
http://xmlrpc.blogg.de/
http://xping.pubsub.com/ping/

Some still have dupes, but only the ones that had multiple ping urls. If anyone wants to whiddle this down further feel free.