I'd like to make a trip out west to either Montana, Wyoming or Idaho in December for activities like cross country skiing, snowmobiling, etc. Any suggestions for a nice resort?
Not out west, but all the winter activities you listed, plus dog sledding, ice fishing, and a fantastic restaurant.
I've been going here for the last 10 years in the summer, and it is wonderful. It's way in the NE corner of Minnesota, just across the lake from Canada, and on the edge of the Boundary Waters Canoe Area Wilderness.
Here is a link that might be useful: Gunflint Lodge