I recently posted on Do we have to ping on all Ping Services.
I very well stated that pinging all services and that too repeatedly can be dangerous for your blog. As I promised there to provide you the accurate list of pinging services that you should use in order to avoid your blog being banned by blogosphere, so here it goes:
Just copy/paste the above links on your WordPress blog. Settings>>Writing>>Update Services and click Save Changes.
Also, this is what I feel about my research on net. If you still want to ping all the update sites, you can search and you will get lots of lots of links. But what I felt is this list is fine as pingomatic individually will ping the other remaining sites. So you need not and should not ping them again.
Let me know what you all feel on this.