UPDATED on April 23, 2015: I've compiled a list of Christmas card challenge blogs. Some of these challenges encourage only Christmas cards; others welcome Hanukkah and winter themed cards as well.
I am not endorsing or familiar with any of these, but thought it would be helpful to have this list....just in case you are thinking of starting. If you are familiar with any others, please let me know and I will update this list.
I intend to start my holiday stamping soon -- not sure when "soon" is, though...
Christmas Stampin' All Year Long
Festive Friday (currently on a hiatus)
Christmas Card Challenges
Crafty Hazlenut's Christmas Challenge
Merry Monday Christmas Challenge
52 Christmas Card Throwdown
Christmas Cards All Year 'Round
ABC Christmas Challenge
One Layer Christmas Card
'Tis the Season
Holly Jolly Christmas Challenge
Winter Wonderland Challenge
Sparkles Christmas Challenge
Muse: Christmas Visions