I think I'm going to take a page out of President Bartlet's playbook. Fans of The West Wing will recall how he ended every meeting with a simple phrase...
He would look around the room, and ask, "Anything else?"
It avoided a lengthy wind-down, gave everyone a chance to bring up anything that might have been missed, and made it apparent that he was done and ready to move on. It seems, perhaps, a little harsh, but as part of a business/professional protocol, it feels like a useful habit.
Then again, I'm not President. So let's see how well this works out ;)