CodeCanyon - Social Locker v1.3.3 - Plugin for Wordpress | 1,76 MB
Social Locker is a set of social buttons and a locker in one bottle. It allows you to lock a part of content on a web page until a user clicks one of the social buttons (Facebook Like, Tweet Button, Google +1) and help you to get more likes/tweets/+1s, traffic and customers!
DEMO:
http://codecanyon.net/item/social-locker-for-wordpress/3667715