Oil filled radient heaters(for sheer safety and efficiency).

NOTE: Not a oil-BURNING heater. Someone recently misunderstood when I said "oil filled" so I add "radient" on to that.

A thermostat is a must. I've had those heat a room to 130F in less than two hours. A low setting and give it several hours to stabalize. A small occilating fan is also a good thing to keep all the temps even(circulating the air to 'spread' the heat properly). The fan can be anywhere in the room, not blowing on the heater, or near the heater.