Simple Welcome Bar is a WordPress plugin that presents a dropdown bar at the top of your site to draw attention to a link or message.
You can also adjust the coloring to compliment your theme or make it really stand out. This is great if you want to be subtle with a new artical or need to warn about an urgent matter. Currently this is setup to stay hidden for one week after the visitor closes the bar.
Download: http://wordpress.org/extend/plugins/simple-welcome-bar/