The Best I know is G4G (Gathering for Gardner Foundation: http://gathering4gardner.org). From 2010, people around the world celebrate the birthday of Gardner and G4G somehow links all of them together. It is up to you at what level you celebrate it. We did it at our own university and students from all departments (science including mathematics, physics, chemistry, and social science) were involved. Just visit G4G and you get many useful ideas and you may share your own ideas.