eisenivan

A lightweight plugin that allows you to place a sitewide alert message in the header of your site. There are options to include a default set of styles (based on Twitter Bootstrap), center your alert, and switch the style class.

Summits Alert

A lightweight plugin that allows you to place a sitewide alert message in the header of your site.

Skysa

Alert your website visitors when you have an announcement for them. The Announcements app allows you to add announcement notices which can display automatically for people who have not yet viewed that announcement. Set how long you want each announcement you add to display and have multiple announcements active at a time.
http://www.youtube.com/watch?v=Zj1uGXX2xrk&hd=1 
<a href="https://wordpress.org/extend/plugins/tags/skysa-apps" rel="ugc">More Skysa App plugins</a> -|||- <a href="https://wordpress.org/extend/plugins/skysa-official/" rel="ugc">Skysa App Bar Integration plugin</a>

Skysa Announcements App

Post pop-up ajax announcements for your site visitors. Rich content, announcement experation date and many other announcement options.

Summits Alert vs Skysa Announcements App