Mark Jaquith

Sends e-mail notifications to a configurable list of addresses when Pages are published, scheduled, or modified. People on the notification list will know what page changed, and in what way it changed (e.g. updated, published, scheduled, trashed, etc).

Monitor Pages

Sends e-mail notifications to a configurable list of addresses when Pages are published, scheduled, or modified.

Huda Toriq

CommentMailer is a WordPress plugin that generates and sends e-mail to your blog’s commenters to tell them that you 
have replied his/her comment on your blog’s comment system. It adds extra options on your blog’s comment form to select 
which commenters you are replying to. Submitting the reply comment will trigger the e-mail generation function thus 
send them automatically. You can customize your own notification e-mail or use the default one.

CommentMailer

Send automated email to your blog's commenters everytime you reply their comments on the blog's comment system.

Monitor Pages vs CommentMailer