Postcrossing is a website which allows people to exchange postcards around the world. Among its more than 550,000 members are over 45,000 Americans, who have so far sent almost two and a half million postcards - a major source of revenue for USPS! Many countries, including the Netherlands, Russia, and the Czech Republic have issued stamps for this amazing website. America should be next!
I designed a mock-up for everybody to look at: