Thanks for all the suggestions and links everyone! I've gone from having no ideas to too many to choose from
Now trying to decide whether to go for smooth icing or the more ruffled royal icing look in that good housekeeping link plus some kind of Christmas scene. I love all the more sophisticated ones with snowflakes and christmas tree shapes too, but lots of visiting children this year so a more child friendly Christmas scene is probably more suitable (even though none of them will probably eat it!).
Stars seem very popular this year, and I thought I was being rather original. (though admittedly I did see the star tree cake) I covered the cake with white ready-rolled, cut out loads of stars with the three star set, sprayed them gold and stuck them all over. I am very pleased with it.