Libnotify is an easy way to display desktop notifications and information in a small dialog. It's used in much opensource apps like evolution , pidgin , etc. It has support for Gtk+ and Qt applications and is desktop independent.
Installation and Configuration
pacman -S libnotify
Now to configure libnotify and use libnotify you can use the gnome or xfce4
pacman -S notification-daemon
pacman -S gconf-editor
then run gconf-editor and select "/apps/notification-daemon/" . There you can configure the notify widget
pacman -S xfce4-notifyd
pacman -S xfconf
For configuration run
Tips & Tricks
You can write your own libnotify display messages easily in python or other langauges. Here is an simple python example.
Note you will need to install the python bindings for libnotify
pacman -S python-notify (communitiy)