CodeCanyon - Facebook Inviter and Content Locker v2.0.3 for WordPress | 1,05 MB
This plugin is a new version of our previous Inviter plugin and has been fully rewritten, featuring a new backend interface, and using the latest Facebook developments to invite friends and post a message on a friend wall.
This plugin enables you to integrate a Facebook Friends Inviter on any blog post or page. Your visitors will have the ability to define the message posted on their friends wall, but you can define as an admin the image and link that will be automatically attached to each message posted on your visitors friends wall.
This plugin also have a way to reward your visitors for inviting their friends, by unlocking a special content (that you can define from the default WP editor), and you can also define how many friends a visitor need to invite before being able to view your hidden content (that can be a coupon code, a secret code, a video, an image, or any content you wish).
DEMO:
http://codecanyon.net/item/facebook-inviter-and-content-locker-for-wordpress/4154741