I've written a new Automator action for displaying a notification center alert in Mountain Lion. You can use it to display a notification when a workflow is complete, to remind you to buy your wife flowers, or anything else that might require a custom alert. I hope you find it useful.
P.S. If you like this, please check out my other Automator actions.
Configuring the action for use. You can specify a title, subtitle, and message
A Notification Center alert displayed by the action
A Notification Center message displayed by the action
Display Notification Center Alert 1.0.1
2012-08-26 - Version 1.0.0
2012-08-29 - Version 1.0.1 - Added support for international and unicode text