Not in the works yet, but this neat concept Google Map Envelopes designed by Rahul Mahtani & Yofred Molk, would be sweet to send out. If you look close in the images above you can see that you are able to track where you are sending your letter from and its destination all through g-mail -- how cool! (via Yanko Design)
Since the above Envelopes aren't quite a reality yet, ( I guess you could custom make your own) here are a few options that still have that long distance connection.
Check out the website -- Map Envelope that prints mailing envelopes lined with your selected location.
and these Stitching Postcards available at Uncommon Goods.