The list below is a working WordPress ping list. The godfather of ping urls in Ping-o-matic. If I were you, I would cross reference this list with the list of services pingomatic pings when you update your blog with a new post. As was mentioned in The Importance of the Ping and XML-RPC-based Push Mechanisms, you do not want to ping the same site more than once for a new post as that could get you labeled as a spammer and banned. Eliminate the duplicates of these services in Update Services under Writing in WordPress.
A Few Working Ping Urls
Some ping urls ping multiple ping servers so pinging the urls they ping separately is unnecessary.
http://rpc.pingomatic.com, http://ipings.com, http://www.pingmyblog.com, http://pingoat.net/ are four such ping urls. Go to each url and check them out. Choose the one that pings the services you want, add it or them to your ping list, cross-reference then eliminate the duplicates in your list.
Check Your List
With any Ping List, you should check that the ping servers you are pinging actually work and are operational. If they are down and dead, you are pinging nobody. Ping List Checker WP Plugin checks your current ping list stored in Update Services under Setting, then Writing in your WordPress Dashboard.
Add your website to MSN through Moreover.com after adding your feed to your myMSN account (it forces MSN to recognize your feed):
Change example.com and sitemap-file.xml with your domain and filename.
If you have any other ping urls that are active, that you have found useful that are not on this list, please post them below so that we can post them in future WP Ping Url Lists and others can benefit.