I am trying to replace an old Lennox thermostat, T874B1076. It has five wires, G, RG & RH, Y1, Y2, X and W1. It controls a two speed cooling system and a gas furnace. What is a good digital programmable thermostat to replace it with?

I would suggest getting a honeywell. Hard to beat. You would be looking for a one heat, two cool compatible stat. Many options out there, but as long as you choose honeywell, you will be happy.