chyron8472 said:

RoccondilRinon said:

I always thought he shouted "NEVER!"

So did I.

ie.:

Vader: Give yourself to the Dark Side. It is the only way you can save your friends. Yes, your thoughts betray you. Your feelings for them are strong. Especially for... sister. So, you have a twin sister. Obi-Wan was wise to hide her from me. Now his failure is complete. If you will not turn to the dark side, then perhaps she will.

Luke: NEVER!

I always thought he said Father as in a warning, in that he had no wish to stab his father in the back and give him a fair chance to turn back to the light side of the force.