Augustus
Res gestae divi augusti
The emperor's own account of his works and deeds. The Latin text is available from Biblioteca augustana, or in small type, with a photo of Augustus' mausoleum, from the website of John Paul Adams. A more idiomatic translation of the whole work, by Thomas Bushnell, is available from the MIT Classics Archives. Another selection, translated by William Stearns Davis (1913), is available from the Internet Ancient History Sourcebook.

Augustus
Epistula ad Gaium filium
The Latin text of a letter from the emperor to his son. (Biblioteca augustana)

Nicolaus of Damascus (fl. first century BC)
Life of Augustus
The Greek life by Nicolaus of Damascus, Herod the Great's teacher (in rhetoric philosopher) and ambassador to Augustus. English translation by Clayton M. Hall (1923).

C. Tranquillus Suetonius
Vita Divi Augusti
The Latin text of a more intimate biography, from the Lives of the Twelve Caesars. John Paul Adams has written an outline of the vita, and an English translation, by Alexander Thomson (1883), is available online from the Ancient History Sourcebook.

P. Cornelius Tacitus
The End of the Republic
From Annales, book 1. Adapted from a translation by Alfred John Church and William Jackson Brodribb. (Internet Ancient History Sourcebook)

Horace, Virgil
Augustan Encomiums
Selections from Horace (Carmen saeculare) and Virgil (Aen. 6.789-800, 847-53) edited by William Stearns Davis (1913), English translation modernized by J. S. Arkenberg. (Internet Ancient History Sourcebook)

John Paul Adams
The Mausoleum of Augustus and the Res Gestae
Cites inscriptions, contemporary descriptions of Augustus' burial, with English translations, a plan of the mausoleum complex, and a list of interments.

Mary R. Lefkowitz and Maureen B. Fant
The Julian Marriage Laws
English translations of Augustan legislation on marriage, procreation, and adultery.

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