St. Cecilia was a 3rd century Roman who was forced to marry a pagan, whom she converted to Christianity. She is said to have preserved her virginity despite her marriage, warning her new husband that her Guardian Angel would be furious if he touched her. Her new husband acquiesced and got baptized. They were both martyred, Cecilia by being beheaded in her own bathtub.
She is the patron of musicians, and apparently possessed a divine singing voice and the ability to play any instrument. She is said to have been able to hear the voices of the Choirs of Angels.
She is associated with the orisha Yemaya and her voodoo counterpart La Sirene. I have also seen her associated with Oshun in Lukumi.
Prayer from my Latin Missal:
Oh God, who dost gladden us with the annual feast of Blessed Cecilia, Thy virgin and martyr, grant that we, who honor her by this service, may also follow the example of her holy life. Through our Lord, etc.
May this sacrifice of propitiation and praise, we beseech Thee, O Lord, through the intercession of Blessed Cecilia, Thy Virgin and Martyr, ever make us worthy of Thy loving kindness.