I noted Hiss earlier as a little stopgap measure to send Growl messages to Notification Center. I used the app for a few days but remained unsatisfied, as every notification is listed as sent from Growl, instead of the proper original app.
Enter Bark. Similar premise, but cleaner. Run Growl and select Bark as the notification style – it takes care of the rest. So far so good, though much of this should be nullified once the Growl 2.0 SDK is fully implemented.