Have you checked out the Moosewood Restaurant cookbooks? They have one called "Moosewood Restaurant Cooks for the Holidays" and they have a bunch of menu suggestions.
In their Thanksgiving section they have a recipe for polenta and roast veggies in place of turkey, or summer squash ravioli (which looked reaaaallly good, but my parents nixed any more food, since we were already set up for a week's worth of leftovers)... and there's a really good recipe for pumpkin pie! (and an apple/pear crisp)
I think they have an actual Christmas dinner section too, but I can't remember what the menu was...