These get thrown around constantly:
(dramatically) "I detect... no evil here!" -- quoted from a paladin NPC. Sometimes we modify it (DM: "You're in the dragon cave. Roll a listen." Player: "5." DM: "You don't think you hear anything." Player: "I detect... no dragon here!")
(dramatically) "I have dire news!" -- quoted from my fighter, upon seeing his dead cohort's father. It is often quoted to mean, "I have dire gnus", so I am thankful that gnus are not statted anywhere in the manuals.
"For great justice!" -- my paladin. Party mates (who invariably hate anything any of my characters do more than once) often cry out "for no great justice" or "for great injustice" or, if they particularly hate me that night, "for great relish (and superlative mustard)".
"What's in the box?" -- quoted from the movie Seven. Don't ask me why we quote this, but any time there's a box, we gotta ask...