There are a variety of Christmas cards available from the Animal Aid Shop, where all money raised goes to help animals.
The Dr Hadwen Trust is a charity that promotes non-animal medical research. They have a range of Christmas cards available.
For original cards that have a vegan theme, CafePress is a great site. Designers sell their own cards directly to the public so you can get unique designs at affordable prices. Similarly, Etsy is another source of designer cards and gifts.
Traidcraft sell a wide variety of fairly traded Christmas items including nativity scenes, cards and wrapping paper.