Make a video and upload it to YouTube.
If you've got friends and family across the country, making a cute video where you announce your engagement is an easy (and fast!) way to spread the word. You could do something simple, using your phones or built-in computer camera, or put together something more elaborate, like a photo collage with narration. Just make sure you tell the really important people -- your parents, your best friends -- before you email the link to everyone.