Do you PostCross? No? You should!
It's a great website that let's you exchange your address with people around the world so that you can send and receive postcards. Kind of like pen pals of days gone by, except that you don't keep exchanging letters with the same person (though you could if you found a connection with someone and wanted to stay in touch). So far we have sent 9 postcards and received 10. The farthest our cards have traveled so far have been to and from China.
We are also using this as a great geography lesson. We are going to get a wall map and start pining all the different countries. It's also a neat way to start an international stamp collection.
You can check out pictures of all the cards I've exchanged on my Gallery page.