Speedboxer

The Comment Approval Notification plugin will send an email to the comment author when you approve their comment. The email sent is fully customizable, with shortcodes, through a settings page.
Please note that this plugin has only been tested with PHP 5.2.x.
A full list of available shortcodes is available <a href="http://mattsblog.ca/plugins/comment-approval-notification/#shortcodes" title="Available Shortcodes" rel="nofollow ugc">here</a>.

Comment Approval Notification

Sends an email to the comment author when their comment gets approved (only if it's held for moderation).

Andrew Nacin

Comment Probation allows you to put a comment author on “probation.”
If you allow comments to automatically appear from authors who already have an approved comment, 
this plugin gives you a bit more control. It lets you approve a comment but place the author 
under probation, meaning that any future comments from that author will need to be moderated again.
When approving a comment, you’re given the option to “Approve” the comment, or “Approve with Probation.” 
If a comment ended up in moderation because the author is on probation, “approving” the comment will 
remove the author from the probation list.

Comment Probation

Comment Probation allows you to require moderation for a future comment by a comment author, rather than having the comment be automatically approved.

Comment Approval Notification vs Comment Probation