Catholic Encyclopedia: St. Justin Martyr
Lengthy article on the life and teachings of the apologist.
http://www.newadvent.org/cathen/08580c.htm

St. Justin the Philosopher
Biography of the martyr. From Alban Butler's Lives of the Saints.
http://www.ewtn.com/library/MARY/JUSTIN.htm

Justin Martyr, Saint
Brief summary of Justin's life and teachings. In the Columbia Encyclopedia.
http://www.bartleby.com/65/ju/JustinMa.html

St. Justin
The story of St. Justin Martyr. Suitable for children.
http://www.tntt.org/vni/tlieu/saints/St0601.htm

The Development of the Canon of the New Testament: Justin Martyr, Saint
Icon, brief biography, links to online works, how Justin Martyr's writings attest to the text of the New Testament.
http://www.ntcanon.org/Justin_Martyr.shtml

The Ecole Glossary: Justin Martyr
Short biography, by Elise M. Bender.
http://www2.evansville.edu/ecoleweb/glossary/justin.html

Saint Justin
Pious meditation on the life of St. Justin Martyr.
http://www.catholic.org/saints/saint.php?saint_id=74

St. Justin the Martyr
Short biography, from the Greek Orthodox Archdiocese of Australia.
http://home.it.net.au/~jgrapsas/pages/justin.htm

Justin
Biography of St. Justin Martyr.
http://www.saintpatrickdc.org/ss/0601.htm#just

Encyclopædia Britannica: Justin Martyr
Article on the Christian philosopher and apologist, from the 11th edition (1911). Includes bibliography. Some scanner errors.
http://www.1911encyclopedia.org/Justin_Martyr

New Schaff-Herzog Encyclopedia of Religious Knowledge: Justin Martyr
Four-page article by N. Bonwetsch on the life and teachings of Justin Martyr, including his Logos Christology. Also has an extensive bibliography. The HTML is readable, but the "image" version (PNG files) is better.
http://www.ccel.org/ccel/schaff/encyc06/Page_282.html

Justinus Martyr, St.
In-depth examination of the theology of St. Justin Martyr, by H. Scott Holland. Brief bibliography, but copious quotations. Requires the ability to view PNG files.
http://www.ccel.org/ccel/wace/biodict/Page_617.html

Introductory Note to the Writings of Justin Martyr
Information on the life and writings of St. Justin Martyr. By A. Cleveland Coxe. From the Ante-Nicene Fathers, vol. 1, American edition.
http://www.ccel.org/ccel/schaff/anf01.viii.i.html

The Martyrdom of the Holy Martyrs Justin, Chariton, Charites, Paeon, and Liberianus, Who Suffered at Rome
Believed to be one of the most trustworthy martyrologies. M. Dods translation, with introduction by A. Cleveland Coxe. From the Ante-Nicene Fathers, vol. 1, American edition. In HTML, with notes, at Christian Classics Ethereal Library.
http://www.ccel.org/ccel/schaff/anf01.viii.xi.html

Patron Saints Index: Justin Martyr
Illustrated profile.
http://saints.sqpn.com/saintj29.htm