Angel of God, my guardian dear...

For the feast of the Guardian Angels, here's a great talk by Professor Peter Kreeft on the Angels according to St. Thomas Aquinas!
I've always been delighted by the whole idea of a Guardian Angel. Kreeft puts an amazing spin on the whole mind-bending doctrine that a superior being would be, as it were, a servant to a creature of a lower order. It is, he says, God's signature: the vocation to humility.
Do you have any stories of your own angelic guardian's service?