by Shaun Scovil on WordPress.org

A Premium Post checkbox is added to the publish metabox in the post editor screen.
Want to add a special message or ad code to your most popular blog posts? This plugin enables you to do just that!
WP-Admin > Plugins.WP-Admin > Settings > Reading and edit your premium post message. template tag inside The Loop.This plugin also adds the conditional tag is_premium_post() for use in your theme template files. You can use it to test if a specific post is marked as premium by passing the post ID (or post object) as a parameter.
Example:
is a premium post!