Ever heard of Valentine, Texas?
Yes, there is a town of Valentine in Texas. For some real fun, you could mail a stamped letter to a post office in Valentine and ask a postmaster to mail it for you.
To make it even more exciting, how about using a pseudo name so that the recipient of your letter will never know who it comes from. That's what I did last year, and it was a lot of fun! It drove the recipient really crazy, as she was unable to figure where the letter came from!
That's a piece of cake, don't you think? I did a google search on Valentine, Texas, and discovered that they receive a large volume of letters in month of January or February. They even have their own postmark design, made for Valentine's. Other than that, it is pretty small town - only 200 people live there.
I would also like to mention that there is also a town of North Pole in Alaska. In fact, I have been there before, as mentioned in a post of December 2005. Perhaps you could have your Christmas cards postmarked there and mail them to your friends? Now, that would be a lot of fun and add more spices!