Best Normally Closed switch for Arduino control?

I would like to control a 12V 250mA light using the Arduino.

But I want the light to remain lit if the Arduino is off or in the middle of a reset.

So I need a controllable switch that is normally closed.

Thanks for any help!

So I need a controllable switch that is normally closed.

I think you mean a relay, most relays have normally open and normally closed contacts. You will have to drive the relay with a transistor and put a diode across the coil.
See:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html