1. Pets in Santa HatsYes, its been done before but pets wearing Santa hats are still adorable. You can also try variations like your puppy holding the hat in his mouth or your cat looking inside an empty Santa hat.
2. Pets "Decorating" the Christmas TreeMost pet owners have many stories of how their pets destroyed...um, helped decorate, the Christmas tree. This year set up the tree early with a few ornaments (just enough to work as a background and entice your pet to action) and let your pet do what he does best. Capture the action with your camera and you'll have a great Christmas card photo!
3. Pets "Kissing" Under MistletoeIf you have two pets who like each other you can set them up for this shot but you will need a helper. Set your pets up in the location you want and get your helper to touch the nose of one with a food the other likes. This should get the other pet to sniff or lick the nose of the first pet. The helper will also hold the mistletoe (preferably plastic mistletoe) over the pets from outside the frame. It may take a few tries to get this shot but it is worth it.
Note - Real mistletoe is poisonous so it is very important to never leave it around pets or children without supervision.