A great source of Christian material is the Christian Classics Ethereal Library which contains a wealth of early church works such as the Church Fathers as well as hundreds of public domain works from over the centuries. CCEL.org is great because of the breadth and organisation of the material. They have hundreds of works of devotional material, theological treatises, biographies, and reference works.
CCEL.org is a well known source of information and someone decided to capitalise on the popularity of CCEL.org by using a similar URL, CCEL.us, for The Evangelical Christian Library, which contains a number of more recent Christian works for which they have received permission to post online. Examples include Billy, A Personal Look at Billy Graham, Evangelical Affirmations by Carl F.H. Henry, and J.I. Packer’s Truth & Power: The Place of Scripture in the Christian Life.
These two sites are both good in the own way and provide a way to read Christian books at work if you have access to the Internet and can’t be seen reading a book 😉