PID Heating Control

So I'm brand new to Arduino, and just starting on my first project. I'm trying to set up an experiment to control the temperature of the air in a small box. I've managed to get a temperature sensor set up and working, but I'm not entirely sure what approach would be best for a heating element. I was thinking some type of coil heater perhaps? Does anyone have a suggestion on what might be most appropriate for this situation? Thank you in advance.

A power resistor switched by a Darlington or MOSFET perhaps? How much power can you get from your PSU? How big a box?

[edit: A tungsten bulb is another possible heat-source, but has the complication of producing mainly heat radiation rather than convective heating - your temperature sensor would need to be shaded from direct illumination I think. ]

In the far past I used low wattage light bulbs to heat up small boxes, I made a couple of incubators as projects in grade school.

Put the bulb in the middles of the box for even heating but also to keep bulb away from the walls for fire safety reasons.

Thanks for the input, a light bulb sounds like it might be a good solution. The box I have right now is small, about 3x3x5 inches, though the final size isn’t critical. My power source is 5V 2000mA.

So, you have 10 watts available. As a starter I'd suggest you use a 12 volt bulb. A 20 watt halogen uses just under 1 amp when powered from 5 volts. Alternatively a 4.7ohm power resistor will do the job. Just make sure it is rated for a dissipation of at least 10 to 15 watts . Although it'll only be dissipating 5 watts you should always under-rate resistors to prevent failure.

These are flexible heaters, good but not expensive. I use for research:

http://www.minco.com/~/media/WWW/Resource%20Library/Heaters/Polyimide%20Thermofoil%20Heater%20Tech%20Spec.ashx