If your light in the outbuilding is powered from the same source (breaker box) as your house, you can get controls from your Radio Shak or from X-10 on the Web that will work.
You plug the light, or whatever, into a little remote-controlled switch that then plugs into the wall outlet. The remote-controller has pushbutton switches that allow you to turn on and off several of these.
This controller sends a digital signal through your house wiring that tells the switch to turn on or off. (That signal has no effect on your other AC devices.)
You can move the controller around, as it only needs to be plugged in to be used.
I have a dog that barks at night. I put a flood light on my porch, pointing in her direction, and a controller by my bed. When I hit the switch she shuts up. (don't know why but glad it works)
[This message has been edited by rpxlpx (edited January 02, 2002).]