You can buy a circuit breaker tracer at a hardware store for about $30.
It has two parts. One part plugs into the wall socket. The other
part you place along the side of each circuit breaker until it indicates
the breaker which controls that wall socket. For light fixtures which
use screw-in bulbs, you can use an adapter.

If you're selling the house, why bother? Let the new owner do it.

Ken wrote:
The previous (original) owner of my house never labeled the circuit breakers
in the breaker panel. Every time I go to change a light fixture or a
receptacle, I have to go thru this trial/error process to find the breaker
to shut off. Now that I'm selling the house, I'd like to have all the
breakers labeled so the new owner won't have the same problems. Is there a
better way to figure out what breaker serves what outlet/light/fixture/etc
other than just flipping each breaker, one-at-a-time until the right circuit
goes dead?