Works

Anacreontic Hymn (Extract)
Translated by Elizabeth Barrett Browning.
http://www.voskrese.info/spl/browning.html#damasc

Apologia Against Those Who Decry Holy Images
Mary H. Allies translation. Three parts. In HTML, with notes.
http://www.fordham.edu/halsall/basis/johndamascus-images.html

Barlaam and Ioasaph
The story of Barlaam and Ioasaph, by "John the Monk". Traditionally ascribed to St. John Damascene, but possibly actually the work of St. Euthymius the Georgian.
http://omacl.org/Barlaam/

Barlaam and Ioasaph
Each chapter in its own file, with links to previous, next, table of contents, or any other chapter. If you are using a graphical browser, this is the online equivalent of a "large print" edition.
http://www.worldwideschool.org/library/books/relg/historygeography/BarlaamandIoasaph/toc.html

An Exact Exposition of the Orthodox Faith
Appears to be the same translation as at CCEL, but without notes. The benefit of this version, at St. Nicholas Orthodox Church, Dallas, is that you can jump to a particular chapter.
http://www.orthodox.net/fathers/index.html

An Exact Exposition of the Orthodox Faith
Each of the four books in its own HTML file, with notes, at Christian Classics Ethereal Library. From A Select Library of Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 9.
http://www.ccel.org/ccel/schaff/npnf209.iii.html

In Defense of Icons
Two excerpts from the writings of St. John of Damascus.
http://www.fordham.edu/halsall/source/johndam-icons.html

Saint John Damascene on Various Subjects
Extracts from the saint's writings on topics including free will and Paradise.
http://home.it.net.au/~jgrapsas/pages/Damascus.html

Three Sermons on the Dormition of the Virgin
Mary H. Allies translation. In HTML, with notes.
http://www.fordham.edu/halsall/basis/johndamascus-komesis.html