I just ordered a new iPod Touch. I took the engraving option, and asked for this to be inscribed on the back:
et cum spiritu tuo
But Apple refused to honor my request. Here's the message I received:
"Inappropriate message text."
So, instead I ordered this to be engraved on the back:
Lord Jesus Christ, Son of God,
have mercy on me, a sinner
It does have the advantage of being a bit more ecumenical than my first choice.