Don't know where you would be flying from, but agree with above answer that NYC is magic. Santa Fe and Taos are also lovely at Christmas with a Southwest/Mexican traditional twist, and opportunity to ski, if thats appealing. Other snow-bound spots that do Christmas nicely are Vermont (sleigh rides, hot toddies in front of the fire of lovely Inns etc) Whistler and Aspen.
Boston is great, and London is also nice at Christmas; gorgeous shop windows, pantomime plays, and if you like shopping, post Christmas sales! almost 8 years ago