There is a wonderful site called
Postcrossing that facilitates postcard "semi" pen pals (semi in the sense that you aren't corresponding repeatedly with only one person, but rather sends a new card to a new person each time). Basically you register on the site and then request an address to send to. They send you and address and then send your address to someone else. The site keeps track of all the cards by tracking numbers - determining how long each card takes to travel to it's destination, how far the cards travel and so on.
Here are the cards from my first batch! (My address is blurred out for obvious purposes)
Australia


This looks like a fascinating creature! If
Thorny Devils did survive in captivity I might be inclined to have one!
Canada


This card is from Canada - I also happen to love
Jean-Jacques Sempé - his illustrations are some of my favorite from the New Yorker Magazine.
Germany


This looks like a wonderful place to study! How historic! I'm looking forward to someday going to Germany and seeing some of wonderful cities there.
Finland


This seriously does look like the coldest place on earth!
Great Britain


Another place I would love to visit - someday I will make it to Great Britain!
United States - Arkansas


Arkansas looks like it has some wonderful natural areas :D