Irssi-nofity-for-Desktop--Notify is a project mainly written in Perl, it's free.
Conversion of the irssi-notify plugin to use the Desktop::Notify DBUS module
This script generates desktop notification bubbles for personal messages and highlighted messages. This script is a adapted version of the well known http://code.google.com/p/irssi-libnotify/
UPDATE: Recently there was some upstream effort to move irssi-libnotify to DBus as well. As by now, it is parently still unusable. But if you like to check them out fetch the "dbus-branch" from their repository. It is using perl::Net::DBus to send messages.