Christian Classics Ethereal Library:
Extremely helpful source of primary texts in church history, Christian spirituality, Christian music, and more
Lectio Divina: Christian Spiritual Authors:
Index page of sources for spiritual reading; many good primary texts in early Christian theology and spirituality.
The Holy See:
Official Website of the Holy See: papal and curial documents in different languages.
"A Hypertext Encyclopedia of Early Church History" (and primary texts)
Christian Art, The Holy Land, Papal Documents
Patristic Texts, The 1908 Catholic Encyclopedia, Hagiography
Christian History: http://www.christianhistorymagazine.org.