I'm somewhat surprised this thread hasn't been started yet, especially with the insomnia crew.
Traditionally, in our family, turkey is for Thanksgiving and a spiral cut honey baked ham for Christmas. Sometimes both, but generally just one.
If it was solely up to me though, I'd much rather have ham as the main course for both holidays, and turkey for leftover sandwiches.
Man, it's hard to top a leftover turkey sandwich with extra mayonnaise and pepper.
As for side dishes, well, the list is too big. But, if I had to pick three, then it would be broccoli casserole, pineapple casserole and sweet potato with raisins and melted marshmallows on top.