Works

Conferences of St. John Cassian
Interviews with the desert fathers about the spiritual life. Hosted by the Order of St. Benedict.
http://www.osb.org/lectio/cassian/conf/

The Institutes of the Coenobia, and the Remedies for the Eight Principal Faults
The Institutes have a great deal of information about monastic discipline and the liturgy of the early Church. This work also includes advice on combatting the eight "thoughts", an earlier form of the seven deadly sins. In HTML, with notes.
http://www.osb.org/lectio/cassian/inst/index.html

The Seven Books on the Incarnation of the Lord, Against Nestorius
Gibson translation, from the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 11. In HTML, with notes, at Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf211.iv.vii.html