This app was mentioned in 3 comments, with an average of 3.00 upvotes
I know you asked for computer wallpaper, but this is my favorite one for a phone! It's a moving image that alternates between a sparkling, rotating Christmas tree and a countdown.
its a live wallpaper on android: https://play.google.com/store/apps/details?id=com.jetblacksoftware.xmastreewallpaperfree
Not very timely but if you celebrate Christmas this one is awesome.
They have a paid version too.