There are a number of automatic ping sites like Ping-O-Matic that will notify other sites that you have updated your pages. If you don't have notification software built into your site, or if there are sites you want to notify that aren't supported by your software, these can be convenient.
However, you do need to understand that many of these sites cheerfully respond to any ping with a positive response even though they have no record of your site in their database at all. Many will just as cheerfully acknowledge a ping referencing a non-existent site. Pinging them may not automatically add your site; you may need to visit them and manually add your information before that ping has any value at that site.
On the other hand, there's some question as to whether these notifications have any value at all. Until very recently, I didn't bother with any of this for my sites and yet when I checked my logs, I found that quite a few of these database sites were regularly spidering my pages anyway.
I suppose it can't hurt. The better places will probably find you anyway through other links, but that may be a hit or miss proposition, so going through the paperwork and being sure you are in their databases, and then following up with pings when you update may have some value.
