For me the Aeron chair. When you're working from home for a year, shelling out a few hundred dollars for a nice chair is worth it. I bought mine from a chair repair shop which usually deals with commercial clients, it is a refurbished chair with some gratis extras added by the owner after we agreed on a price ($450). I like that I bought it from a chair repair shop because I can always go back there if there is a problem but I have not had a problem.