Divine Office: Read the Liturgy of the Hours in words or listen to hymns, psalms and readings. Can be played on your computer or downloaded to your mobile device. Also has background information on this devotion.
Vatican: Extensive library of church documents, much more
United States Conference of Catholic Bishops: daily Mass readings, Catechism of the Catholic Church, New American Bible, much more
EWTN: Extensive library of church documents, TV schedule, more
Word On Fire: Blog, homilies and other resources by Fr. Robert Barron, author of Catholicism series
CatholiCity: "The Catholic Church Simplified." Many resources, from Catechism to lists of good sites to news