Here is the O Antiphon for today:
Dec. 20 - O Clavis David: “O Key of David, O royal Power of Israel controlling at your will the gate of Heaven: Come, break down the prison walls of death for those who dwell in darkness and the shadow of death; and lead your captive people into freedom.” (cf. Isa 9:6; 22:22)
Also see my previous post, "What Are the O Antiphons?"
Pax Christi,
phatcatholic