Snailmailr: send physical mail from the web
Snailmailr costs a little bit more than a stamp, but saves you the time of picking up stamps or printing them yourself. Including the cost of envelope and paper, $1 is a pretty reasonable price to pay. There's a little bit of an extra cost, though, if you don't want to be tacky: you can remove the Snailmailr logo from your envelope for an extra 15 cents. Everything else about Snailmailr looks good: they allow color images in letters, and they address environmental concerns by using recycled paper and buying carbon offsets.