I adore stamps that promote adoption of animals from shelters. The Australia postal service published a series of animal stamps in 2010; a full summary is available here.
According to estimates provided by the Humane Society of the United States, 6 to 8 million animals enter U.S. shelters each year. Only half of those animals are adopted. That means the other half, even healthy animals, are euthanized. Please remember to adopt - don't shop - when you are looking for a four-legged friend for your family.