On December 2, 2006, we visited Marble House and The Breakers mansions in Newport, RI. These two along with the Elms are decorated for Christmas. Surprising the mansions weren't crowded. In Marble House, a free taped guided tour is provided with your admission. In the Breakers, the tour is self guided. By far the Breakers had much more elaborate Christmas decorations and should not be missed. Be sure to check out The Breakers gift shop for unique gifts. It was very enjoyable visit! Photos are only allowed in The Breakers main hall.
See the official Preservation Society of Newport web site for more information:
Newport Christmas

On November 22, 2008, we visited the Astors Beechwood mansion in Newport, RI. The tour consisted of 20 minutes that you can tour the various rooms on your own. In each room was a costumed guide that recounted information about the people, furniture, history, etc. Each person kept in character as they answered questions. The various guides in each room had fascinating stories but we felt rushed to see all the rooms as it had been quite a long time since we visited the mansion. Each room was decorated with Christmas related decorations.

Next all were invited to the ballroom where the costumed guides put on a show for 40 minutes. The show consisted of piano playing, singing Christmas carols, dancing, playing popular parlor games of the time, etc. (all keeping with the time period of the house). Various audience members participated in all the events except the initial Christmas carols. So if you are shy avoid sitting in the front rows and you won't be asked to participate!