The kids and I signed up with postcrossing this afternoon. We'll send and receive post cards around the world! Our first five cards are being mailed to people in Russia, The Netherlands, Belarus, Germany, and Missouri. (There is an option to receive cards only from people outside of your home country, but I thought it'd be nice to have a quicker postal turnover rate for some of them.) The site maps everything for you, and just looks really cool. Bonnie plans on starting a little scrap book and mapping all of our cards on the wall.
Hopefully the arrival of these cards leads to pop-up geography lessons because the kids want to learn more about each country or state. That's my little unschooling dream at any rate.