Do you want to put a gift card for your Kindle, Nook or Kobo ebook in your Christmas cards? A company called Livrada can do it for you. They assign codes to your books, print the cards and then the books can be redeemed with the cards.
Panzer says, "Be warned. This is expensive and there are minimum orders of 500 cards."
Don't know 500 people for Christmas cards? Give them away at conferences, events and as giveaways for book promotion.
If this sounds interesting to you, tootle over to Gift Card for your ebook.