Michael, whose name means “Who is like God?” is the Angel who rose up against satan. He is our defender against the “wickedness and snares of the devil.”
Gabriel’s name means “Strength of God” is the Angel who announced to Zachariah the upcoming birth of St. John the Baptist and to the Virgin, God’s plan for her to be the Mother of God. Tradition speculates that it was also he who appeared to the shepherds and announced the Savior’s birth.
Raphael, “Medicine of God” is the Angel who ministered to Tobias on his journey.
For more on these Angels, see Catholic Culture’s excellent Article.