Two — one to change the bulb, and one to write a song about how good the old light bulb was.
or
Your wife comes back to you, your dog returns to life and you get out of prison.
or
That's proprietary information. The answer is available from AT&T on payment of license fee (binary only).
or
They charged one - and let the other one off.
or
10. One to hold the bulb and nine to rotate the ladder.
or