Let’s turn our attention now from sinner to saint. On this day many churches observe the Feast of St. Michael and All Angels, called in England “Michaelmas”. In Christian tradition Michael is the chief of the angels–spiritual beings who act as messengers and agents of God. Michael is especially associated with spiritual warfare and defense against the invisible forces of darkness.

Prayer (Anglican):
O EVERLASTING God, who hast ordained and constituted the services of Angels and men in a wonderful order: Mercifully grant that, as thy holy Angels alway do thee service in heaven, so by thy appointment they may succour and defend us on earth; through Jesus Christ our Lord. Amen.

Prayer (Roman Catholic, short version):
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.

Further reading:
Historic UK
English Book of Common Prayer Online.
Tradition in Action (additional prayers from the Roman Catholic tradition).