At your next conference, business meeting or retreat, don't give out attendance prizes.  Give out idea prizes instead in an "Idea Lottery."

From Creativity expert Michael Mihalko:

Have an “idea lottery,” using a roll of numbered tickets. Each time a person comes up with a creative idea, he or she receives a ticket. At the end of [the event], share the ideas ... and then draw a number from a bowl. If the number on anyone’s ticket corresponds to the number drawn, he or she gets a prize.

This is an easy-to-implement idea that could add some fun and interest to your next group gathering.  Just make certain you prepare your audience before the event so they can get their thinking caps on.