Inverter Design - What DC input voltage for most efficient DC to 120VAC inverter
So once again, in an inverter design without a transformer, what DC
  input voltage would result in 120VAC naturally?


If you use a H bridge output then you need a DC supply capable of delivering the peak voltage of a 120 V AC sinewave. That's about 170 volts but you'll probably need a couple of volts more to account for volt drops.