Facebook Likes You! is simple plugin which makes it easy to add Like Button and widgetable Like Box. Google +1 isn't a problem too!
This plugin adds a Like-Button wherever you want on your blog. Before or after the content as well as a sidebar-widget. And many more!
Add the Facebook Like and Send Button to your wordpress. Very simple configuration.
Like Gate allows you to reveal some hidden/secret content when the user likes the article. Therefore increasing the likeness of your articles.
Facebook Like Lock for WordPress. Locks your content and user can unlock by clicking on like button.