Announcement Plugin?

I’m looking for a plugin that would let me put an announcement box under my navigation (http://www.raffledog.com). I see it around on websites and just realized that youtube uses something similar to what I’m looking for. Picture below:

http://raffledog.com/googlepic.jpg

The green box in this picture is what I’m looking for. When a user clicks the X it disappears and the body of the page moves up. Seems simple but I can’t find it anywhere. Thanks!