Ping Service is basically a way to notify Google and other search engines that your blog or website has been updated, and requesting them to index or reindex your website. It is one of few ways that can get your pages indexed by search engines faster. Here is the article that lists few other ways that get indexed by Google fast.
Now, it is a good idea to use one of ping service websites when you have update your website, but you should never overdo it. Usually, you should wait at least 5 hours before pinging them again.
In this article, I am going to share a list of high PR ping service sites that you can use. Remember, you only need to pick one of them. Usually, higher PR ping service sites tend to be more effective with low PR.

List of High PR Ping Service Sites

Site List	PR
blogsearch.google.com/ping	7
twingly.com/ping	7
pingomatic.com/	6
mypagerank.net/service_pingservice_index	6
icerocket.com/c?p=ping	6
blo.gs/ping.php	6
auto-ping.com/	5
bitacoras.com/agregador/enviar	5
feedshark.brainbliss.com/	5
blogpingtool.com/	4
pingler.com/	4
pingmyblog.com/	4
totalping.com/	4
ping.in/	4
rpc.weblogs.com/	4
bulkping.com/ping/index.php	3
googleping.com/	3
pingoat.net/	3
blogs.yandex.ru/pings	2
blogbuzzer.com/	2
backlinkping.com/	2
pingbomb.com/	2