Radek Mezulanik

Show the number of pending posts waiting for approval in the admin menu, if any. Also automatically supports custom post types. Sends email notification of posts pending review.

Zedna pending post indicator and notifier

Display number of posts waiting for approval in administration. Send an email about waiting approval, approved/rejected post.

fulippo

WP Status Change Notifier allows you to notify selected users when posts’ status are changed.
What it does:
<ol>
<li>Notify selected users when new posts are awaiting for approval</li>
<li>Notify contributors when posts are approved or refused</li>
</ol>

WP Status Notifier

WP Status Change Notifier notify users about posts status changes.

Zedna pending post indicator and notifier vs WP Status Notifier