When you say Christmas, do you mean plants that will be flowering or have berries etc, at Christmas, or just for over winter generally? Also - how big is your pot?Things like Hellebores will be looking good - some flower at that time. They have distinctive foliage so you could team them with an evergreen grass - possibly a variegated one - for a contrast. Many of the Carexes are ideal. You can also plant things which wouldn't be suitable long term - like Cornus for example - which have coloured stems and provide vertical height, but you couldn't leave them permanantly in the container as they get too big. You can add winter flowering pansies for extra colour, and bulbs for late winter/early spring to continue the look.Someone recently talked about a similar planter [it was shown on one of the links here I think] They were copying it and asked for some advice. I only know about it because I posted on it. I'll see if I can find it.