Ever heard of lutterfu? Me neither til I came across this website earlier today, filled with templates and instructions for a snail-mail letter, envelope and seal all in one--write your letter on one side, fold inside-out along the pre-marked lines, seal with a stamp placed in the upper right corner, address and you are good to go!

I'm printing one out right now to test it. This is so cool!

UPDATE: I'm actually working with the original designer right now to make these available in my shop. So excited!