Display a notification with AppleScript
Growl has an AppleScript dictionary. I didn't find any way to show a single notification in Notification Center, but they are shown in it by default you've enabled forwarding all notifications.

tell application id "com.Growl.GrowlHelperApp"
    register as application "Scripts" all notifications "test" default notifications "test"
    notify with name "test" title "title" description "description" application name "Scripts"
end tell