Make-a-Flake - definitely one of my favorites. Do you know how many kids do NOT know how to cut out a paper snowflake? It really is sad. This is a virtual one but you can save the image, send it, share it and you can probably create fancier snowflakes than you could in real life. Very fun to see what your "cuts" will create. (and not paper scraps on the floor!) This would be a fun activity to do with students and then make the actual paper ones. I actually like to do "snow" activities in January since there are plenty of Christmas things to do in December. And in Texas we tend to get our actual snow in January or February.
Virtual Cookies? Here are two sites.
Old Fashioned Christmas from Theoworlds.com. I like the simplicity of this one. You can email it, get the link, get the code to embed but there is not an easy way to exit and go to the beginning other than to reload the page. Still fun.

From Sprint there is SprintSweets and the Gingerbread Man with Everything. Save it, share it, send it. Decorate with icing and candies. Easy to start over but you can't just undo a step. It is all the way back to the beginning if you mess up and want to fix it. I do like how he is on the little cookie sheet though! Cute!
Decorate a Christmas Tree Cute, simple drag and drop, can add snowfall. Save or print image. This does have ads though (boo!). The way this image comes out you could photo edit and add your own message on the right side of the tree.
Christmas Tree I like this one. No ads. Simple drag and drop. No save or share but you could snip it. Turn off the lights and the fireplace and tree glow. Nice for the Smart Board. Reload page to do again.
From Castle Arcana there are other links like Build a Snowman, Musical Christmas Tree, or how about The Christmas Carol for Guinea Pigs. Okay, maybe not?
One hint to searching for fun to do on the Smart Board is to search with the word "interactive". You will find more that will work on your interactive whiteboard. There are lots of Smart Board lessons for Christmas fun also out there. You won't be at a loss for things to do during this last week before the Christmas break.
Have fun!