You have to check out this very cool website.
Basically, you type in a message, and it finds satellite images of buildings around the world that look like each letter in your message. Then it generates a link that you can copy and email to your friends. There is also an option to send as an e-card or a MySpace e-card.
Here's an example link I created this morning.
If you wanted to take this a step further with your kids or students, you could then click on a letter to view the building on a Google map.