Ninja Popups combines a professionally designed popups to convert visitors on your site/blog into taking an action 

whether its subscribing into your newsletter, offering a discount/coupon for leaving customers, or locking content until 

they share you will increase your subscriber count and social signal of your site/blog.

Product page: http://codecanyon.net/item/ninja-popups-for-wordpress/3476479

This plugin has been fully nulled, to install simply upload it to your host like you would any other wordpress plugin.