Go to WordPress Dashboard > Options > Writing and paste the following URLs under Update Services field.

List of WordPress Ping Services

http://1470.net/api/ping
http://api.feedster.com/ping
http://api.moreover.com/ping
http://api.moreover.com/RPC2
http://api.my.yahoo.com/RPC2
http://api.my.yahoo.com/rss/ping
http://bitacoras.net/ping
http://blog.goo.ne.jp/XMLRPC
http://blogmatcher.com/u.php
http://blogsearch.google.com/ping/RPC2
http://bulkfeeds.net/rpc
http://coreblog.org/ping/
http://mod-pubsub.org/kn_apps/blogchatt
http://ping.amagle.com/
http://ping.bitacoras.com/
http://ping.blo.gs/
http://ping.bloggers.jp/rpc/
http://ping.blogmura.jp/rpc/
http://ping.cocolog-nifty.com/xmlrpc
http://ping.exblog.jp/xmlrpc
http://ping.feedburner.com/
http://ping.myblog.jp/
http://ping.rootblog.com/rpc.php
http://ping.syndic8.com/xmlrpc.php
http://ping.weblogalot.com/rpc.php
http://ping.weblogs.se/
http://pingqueue.com/rpc/
http://pinger.blogflux.com/rpc/
http://pingoat.com/goat/RPC2
http://rcs.datashed.net/RPC2/
http://rpc.blogbuzzmachine.com/RPC2
http://rpc.blogrolling.com/pinger/
http://rpc.icerocket.com:10080/
http://rpc.pingomatic.com/
http://rpc.technorati.com/rpc/ping
http://rpc.weblogs.com/RPC2
http://services.newsgator.com/ngws/xmlrpcping.aspx
http://topicexchange.com/RPC2
http://trackback.bakeinu.jp/bakeping.php
http://www.a2b.cc/setloc/bp.a2b
http://www.bitacoles.net/ping.php
http://www.blogdigger.com/RPC2
http://www.bloglines.com/ping
http://www.bloglot.com/rpc/
http://www.blogoole.com/ping/
http://www.blogoon.net/ping/
http://www.blogpeople.net/servlet/weblogUpdates
http://www.blogroots.com/tb_populi.blog?idhttp://1
http://www.blogshares.com/rpc.php
http://www.blogsnow.com/ping
http://www.blogstreet.com/xrbin/xmlrpc.cgi
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/

Did I missed some service(s)? If yes, feel free to add those URLs as a comment below and I will include those URLs to the list.