C. Suetonius Tranquillus
Vita Divi Iuli
Latin text of the most intimate of ancient biographies, hosted by the Ad Fontes Academy. An English translation, by J. C. Rolfe (Loeb, 1920), is now online at the Ancient History Sourcebook.

Plutarch
Life of Julius Caesar
Translated by John Dryden. (MIT Classics Archive)

Plutarch
Life of Mark Antony
Translated by John Dryden. Includes description of Caesar's assassination. (MIT Classics Archive)

Plutarch
The Assassination of Julius Caesar.
Described in Plutarch's life of Marcus Brutus, as translated by John Dryden.

Julius Caesar
War Commentaries
Caesar's account of his campaign in Gaul and the war against Pompey, translated into English by W. A. McDevitte and W. S. Bohn (1869). Includes contemporary accounts (not by Caesar) of the campaigns in Egypt, Africa, and Spain. Also available from the MIT Classics Archive. The Latin texts of all five Commentarii are online at the Ad Fontes Academy. See also The Caesar Machine, which gives hypertext glosses (in English) for the Latin text of De bello gallico 1-4.