Set up your WordPress to ping a list of aggregators automatically. Go to Options>Writing and at the bottom of page you will see:

Update Services

When you publish a new post, WordPress automatically notifies the following site’s update services. For more about this, see Update Services on the Codex. Separate multiple service URIs with line breaks.

Add your own list there. There are many lists that can be found with Google but i recommend this link with a great list:

XML-RPC Ping Services - A comprehensive list of blog pinging services.

After a fresh WordPress installation you should do this every time you create a new blog.