BibliaClerus. Ever wondered what the Church Fathers thought about a particular Bible verse? Find it here. Want some Cross references from the Fathers to Sunday's liturgy? It's here. Need to access the texts of the Magisterium? Right here. Need to look up something in Canon Law? Here again. You can even download the entire site of BibliaClerus.
This is a beautiful resource for the faithful from The Congregation for the Clergy at the Vatican.