Picnik is free and they let you edit all of your photo's online in one easy place. I purchased the premium edition which only cost $24.95 for the year and I use it to create all sorts of collages and free prints for here on my blog.
Here are some examples they have available in the seasonal section below:
Frost frame theme
Holiday texture - Sparkles
frost and snow
So much fun and so easy.
Would be great for Christmas cards.