Distinguished Professor of History and Religious Studies
Patristic Resources
Saundra Lipton has compiled a great set of resources on Christian groups large and small.
And for monasticism, see the site of the monastery of Christ in the Desert.
The Desert Fathers.
For Gnosticism and the fringes of Christianity, see the many texts collected by the Gnostic Society Library.
The Gospel of Thomas, with extensive commentary.
Pseudo-gospels and other texts on the Christian fringes
The Sacred Texts library has a wide selection of Christian documents and scriptures, as well as much else on other religions and faiths.
Beliefnet
Christianity Today.
Books and Culture
Christian Century magazine
Since I work on Roman Catholic issues, I will include a number of Catholic sites here. One good place for Catholic resources is Peter’s Net. Other general Catholic sites, with lots of links, include Catholic.net and Catholic.org. You can also look here and here for general launch sites. Look here for the US church's official positions; and for some radical and liberal voices, check out the National Catholic Reporter.
For Anglican and Episcopalian resources, see
Anglicans online.
Episcopal Life
Church Times (UK)
The Anglican Book of Common Prayer.