This PubSubHubbub plugin from code.google.com is an easy way to let the people know when your blog is updated in real-time. Its quickly gaining adoption and is already being used by Google Reader, Google Alerts, FriendFeed etc.
You can use it in your WordPress site. Simply install and activate PubSubHubbub plugin. Optionally you may select custom hubs under PubSubHubbub Settings from your admin area dashboard. Learn more about PubSubHubbb at Google Code