WordPress' Update Services allow you to let other people know you have updated your website. WordPress automatically notifies popular update services that you've updated your blog by sending an XML-RPC ping each time you create or update a post.
When WordPress contacts these updates services, they process the ping and update the indices (database) with your update. When people are using sites like Technorati or Sphere, people can see your most recent additions and changes.
Otherwise you can insert your own ping services in the Settings => Writing => Update Services in the admin panel of your WordPress installation. Below is a list of some of the popular update ping services on the Internet.
XML-RPC Ping Services
http://rpc.pingomatic.com http://api.feedster.com/ping http://api.moreover.com/RPC2 http://api.moreover.com/ping http://api.my.yahoo.com/RPC2 http://api.my.yahoo.com/rss/ping http://www.blogdigger.com/RPC2 http://www.blogshares.com/rpc.php http://www.blogsnow.com/ping http://www.blogstreet.com/xrbin/xmlrpc.cgi http://bulkfeeds.net/rpc http://www.newsisfree.com/xmlrpctest.php http://ping.blo.gs/ http://ping.feedburner.com http://ping.syndic8.com/xmlrpc.php http://ping.weblogalot.com/rpc.php http://rpc.blogrolling.com/pinger/ http://rpc.technorati.com/rpc/ping http://rpc.weblogs.com/RPC2 http://www.feedsubmitter.com http://blo.gs/ping.php http://www.pingerati.net http://www.pingmyblog.com http://geourl.org/ping http://ipings.com http://www.weblogalot.com/ping
* An alternative is Feed Shark (Blog and Ping), which pings over 60 services for free.
* Feedburner users can use the Feedburner Pingshot service, which will alert most popular ping services.
* If you're interested in manual configuration, have a look at the WordPress compressed ping list.
* Check Vladimir's WordPress Ping List, manually checked and updated
* The Smart Update Pinger (requires registration) and the MaxBlogPress Ping Optimizer plugins provide future post pings, logging, and avoid sending any ping notification when editing previously published posts. The Smart Update Pinger also provides correct extended ping request handling.