Should a Christian ever lie?
God hates lying. Proverbs 16:6.
Jesus suggested that it was appropriate to break the "rules" if it involved a greater good or need. Mark 2:23-28 (Jesus' disciples are eating grain on the Sabbath, and Jesus cites David eating the priests' consecrated bread when he and his men were hungry to justify the practice).
I've heard a pastor go so far as to say that if the Nazis came to your door, and you were hiding Jews, you would be obligated as a Christian not to lie about it. I've also read Bonhoeffer say that this thought is 'grotesque,' and that you should tell a 'robust lie.'