The Emperor Julian: An excellent site giving a history of the Emperor Julian's life. Highly recommended!
The History of the Decline and Fall of the Roman Empire: Gibbon's classic, available as an electronic text. Chapters with information on Julian include XIX, XXII, XXIII, XXIV and XXV.
An inscription from Jerusalem carved during Julian's reign: Description and photograph of an inscription on the Western Wall, inspired by Julian's attempt to restore the Jewish Temple there.
Two Orations of the
To the Sovereign Sun and To the Mother of the Gods
Emperor Julian's Rescript on Christian Teachers - Julian's law
forbidding Christians to teach from Homer and other Pagan sources they did
not believe. Link also includes a short text of Julian's letter to Atarbius,
forbidding punishment of Christians for their beliefs.
The Hermetic Fellowship Website: An excellent site concerning the ancient Mystery traditions of the ancient world. This site has many great resources and is also highly recommended!
Julian and the Jews - Ancient texts regarding Julian's attempt to rebuild the Temple of Jerusalem.
Sallustius' On the Gods and the World - A pagan religious manual written by one of Julian's generals. (Includes other links to the same ancient text.)
The Emperor Julian and Neoplatonism - Am article by Madeline Clark regarding Julian's involvement with Neoplatonic philosophy.
The Platonic Creed - An article from "Shrine of Wisdom" magazine referencing quotes from Julian