How to show a GUI message box from a bash script in linux?

In many Linux distros the notify-send command will throw one of those nice perishable notifications in the top right corner. Like so:

notify-send "My name is bash and I rock da house"

B.e.a.utiful!

I believe Zenity will do what you want. It's specifically designed for displaying GTK dialogs from the command line, and it's available as an Ubuntu package.