I was in need of a top bar for a WordPress site to communicate news and updates to users. In doing some research there are a lot of options. I ended up settling on wp-topbar
http://wordpress.org/extend/plugins/wp-topbar/
This plugin is really easy to use and has some great features in the admin section. It allows you to set style and other granular items. I specifically like the wait time and the ability to add images right from the admin. One great little feature is the ability to preview the top banner in the admin section.