This is my favorite prayer. I like to pray it before bed each night.

Saint Michael the Archangel, defend us in battle, be our protection against the malice and snares of the devil. May God rebuke him we humbly pray; and do thou, O Prince of the Heavenly host, by the power of God, thrust into hell Satan and all evil spirits who wander through the world for the ruin of souls. Amen.

Sáncte Míchael Archángele, defénde nos in proélio, cóntra nequítiam et insídias diáboli ésto præsídium. Ímperet ílli Déus, súpplices deprecámur: tuque, prínceps milítiæ cæléstis, Sátanam aliósque spíritus