Calligraphers and artists from around the world are invited to participate in the 22nd annual Graceful Envelope Contest, conducted by the Washington (DC) Calligraphers Guild and the USA National Association of Letter Carriers. This year's theme is Communication. You can read here the details.
Even if you do not participate, it is a great pleasure and a source of inspiration to have a look to the winners. They look very professional, even the children's envelopes!