Institutes of the Christian Religion
E-text as translated by Henry Beveridge.
http://www.reformed.org/books/institutes/

The Necessity of Reforming the Church (1543)
An English translation of the complete text.
http://www.swrb.ab.ca/newslett/actualnls/NRC_ch00.htm

Treatises on Predestination
Text of English translation by Henry Cole.
http://www.reformed.org/documents/calvin/calvin_predestination.html

On the Christian Life
Translation by Henry Beveridge
http://www.ccel.org/ccel/calvin/chr_life.titlepage.html

Of Prayer
Subtitled "A Perpetual exercise of Faith. The Daily Benefits Derived From It."
http://www.ccel.org/ccel/calvin/prayer.titlepage.html

On Hundred Aphorisms
A list of concise statements taken from Calvin's Institutes.
http://www.ccel.org/ccel/calvin/institutes.v.html

Preface to the Genevan Psalter, 1565
Discussion of music and singing in the church liturgy.
http://www.ccel.org/ccel/ccel/eee/files/calvinps.htm

Consensus Tigurinus
Document written by Calvin and Bullinger on the sacraments.
http://www.creeds.net/reformed/Tigurinus/tigur-bvd.htm

The Geneva Catechism
A catechism or a little "Confession of Faith" published by Calvin in Geneva in 1536.
http://www.ondoctrine.com/2cal0504.htm

Short Treatise on the Lord's Supper
John Calvin's treatise on the Lord's Supper and its true institution, benefit, and utility.
http://www.the-highway.com/supper1_Calvin.html

Christian Classics Ethereal Library: John Calvin
Includes biographical information, texts of commentaries, sermons, Institutes, "On Prayer", and "On the Christian Life".
http://www.ccel.org/c/calvin/

Calvin's Commentaries
The complete commentaries of John Calvin online.
http://www.ccel.org/ccel/calvin/commentaries.i.html