Snail mail is still a pretty great way to send letters, but many of us use it so seldom that we don't have any envelopes lying around. For those occasions, here's a quick way to fold your letter into its own envelope.
Sometimes you don't have any envelopes, and even more often you probably find yourself with the wrong size envelope. Of course, you could always just head to the post office, but it hardly seems worth it for the one envelope you need right that second. With just a few clever folds, you can turn your letter into its own envelope, write the address on the back, stick a stamp on it and go. Of course, we wouldn't recommend this method if you're sending something sensitive like a cheque, but if it's just a friendly letter to Grandma, this will do in a pinch. Hit the link for the step-by-step instructions.
Envelope-free letter sending (Snail-Mail origami) [Instructables]