First off, what a great idea!

My favor idea would be to make little mini "megaphones" (those cone shaped things cheerleaders use) and put "Thank You" with your orgainization on the side. That way it's something small and inexpensive (I made mine out of card stock or sometimes Oriental Trading will have them available) and something they can keep because they will know who it was from!

Best of luck with your organization's recognition dinner!