-Send notifications to subscribed users when a comment reply is posted
-Send a notification e-mail after new content was added
-Send a notification when a page is edited
In order to place the URL of the node in the email, you have to construct the URL with the available tokens. For example: [node:site-url]/node/[node:nid]
A2: Use [node:node-url] (D6 + Rules 6.x-1.4 + Token 6.x-1.15)
http://drupal.org/project/mimemail can add HTML to your email.