Works

Letter to Flavian
Tanner translation.
http://www.dailycatholic.org/history/4ecumen1.htm#The letter of Pope Leo to Flavian, bishop of Constantinople, about Eutyches

Letter to Flavian, Commonly Called "The Tome"
Charles Lett Feltoe translation, from the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 12. With notes, at Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf212.ii.iv.xxvii.html

Letters
Charles Lett Feltoe translation, from the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 12. Each letter in its own file, with notes and links to contents, previous, next. At Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf212.ii.iv.html

Sermon 85
On the Feast of S. Laurence the Martyr. With notes. At Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf212.ii.v.xliv.html

Sermons
Charles Lett Feltoe translation, from the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 12. Each sermon in its own file, with notes and links to contents, previous, next.
http://www.ccel.org/ccel/schaff/npnf212.ii.v.html

The Tome
Henry R. Percival (editor), William Bright (translation). From the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 14. Included in this volume on the ecumenical councils because Leo's letter was approved at Chalcedon. With notes, at Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/npnf214.xi.vii.html