Well, one idea might be for the boss to take them out to a nice dinner or lunch. Or perhaps have something brought in. During the lunch the boss or supervisor could thank everybody for their efforts and team work.
Another nice idea are bonuses or gifts around the holidays. Some companies might not be able to pay bonuses, but it's certainly nice to get a gift as an alternative.
Most people like to be praised, especially after they work hard. So it's a great idea for bosses to take the time and energy to do so. It makes everybody on a team feel more valued and appreciated.