I make the mashed potatoes, with butter, sour cream and creamed cheese the day before. Then I put them in a buttered crock pot container, and stick them in the fridge overnight.
Next morning/day, you put them in the crock pot to warm up while you do the turkey, gravy, veg, etc.
Considering doing the potatoes is my least favourite part, it's nice to get it out of the way the day before.
There are quite a few recipes online. Almost all call for sour cream and creamed cheese, so they must be vital in some respect.
ETA:
http://whatscookingamerica.net/Vegetables/PotatoesMakeAheadMashed.htm