I’ve been searching for a while for an easy to install email notificaton plugin. I finally found a plugin today at watershedstudio.com. It took about 15 minutes to install, but a little longer to test as it only sends notifications on publishing and not on updating, even though an option shows up on the editing page to notify subscribers when you are editing an entry.
The plugin allows people receiving notifications to unsubscribe as well.
Aside from the update vs. publish confusion, the plugin works really well. Download it here if you have been wanting to add this functionality to your WordPress site.