I want to replace my old thermostat with a new programmable one there are 2 wires coming out from the wall a black and a white wire I have gas heat and baseboard heating , which model of thermostat do I use to replace my old thermostat.

Gas hot water heat (boiler) with baseboards? Many thermostats will work. I suggest honeywell. Most likely, with only two wires, the new thermostat will require batteries to operate. If the batteries die, the heat dies. However, I don't recommend using a programmable thermostat for hot water heat with baseboards, as radiant heat takes a lot longer to bring up temp of house than a forced air system. As a rule of thumb, stick with a constant setting on the thermostat with hot water heat. In my experience, programmable stats just don't work reall good with boiler systems.