Ninja Kick: Sliding Panel is a premium WordPress plugin that adds hidden off-canvas sidebar with push or sliding animation on your WP website. Extra content added to sliding panel will wait for it’s time to reveal! You can utilize this plugin in so many ways. For example add navigation, social feeds, offer an subscription, display ads, registration or contact form, shopping cart etc. Popups are so 2009!

Demo: http://codecanyon.net/item/ninja-kick-sliding-panel-for-wordpress/6796296