Scroll Popup allows you to slide popups from all four corners of your website. You can choose in which corner you would like the popup to appear and also the direction you would like the popup to slide from. Display just about any type of content within popups: banners, adsense, contact forms, images, videos, shortcodes, newsletter forms, and anything WordPress editor allows.
Demo: http://codecanyon.net/item/wordpress-scroll-popups-plugin/10869934