It is recommended to add a list of Ping services to your WordPress Blog. They allow you to automatically notify the blog directories and search engines that your blog has been updated with a new post or article. WordPress comes by default with “rpc.pingomatic.com”. I won’t add that one to the list, so you don’t have duplicated pings. Just go to “settings”, then “Writing” and on the bottom (Update Services) you will find the box to paste this list.
Make sure you don’t delete the url that comes by default with WordPress (rpc.pingomatic.com) and you add the following list, just after the “pingomatic” url. This list is updated for year 2009. I don’t recommend having a BIG list… I think that having between 5 and 10 popular ping sites is fine. The problem of having a big list is that every time you post, it takes very long to ping, because the list is large. The other problem with a large list, is that you will probably have small and no popular sites that might go offline soon or late. If these sites go offline, you can have problems when you post. So, below is a list of the most popular ping sites, like I said before, remember to paste these sites after the “pingomatic” url.