Letter to Vergilius of Arles
Found in the Venerable Bede's "Ecclesiastical History." At CCEL.
http://www.ccel.org/ccel/bede/history.v.i.xxvii.html

Letter to King Ethelbert
Excerpt from the Venerable Bede's "Ecclesiastical History." At CCEL.
http://www.ccel.org/ccel/bede/history.v.i.xxxi.html

The Pastoral Rule
From the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 12. Four parts, each in its own HTML file, with notes. Links to table of contents, previous, next. At Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf212.iii.html

Epistles, Books One through Eight
Each book in its own HTML file, with notes, at Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf212.iii.v.html

Selected Epistles, Books Nine through Fourteen
Barmby translation. Each book in its own HTML file, with notes, at Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf213.ii.i.html

Moralia in Iob, Books One through Five
James J. O'Donnell translation.
http://www9.georgetown.edu/faculty/jod/gregory.html