Interlinear texts consist of a text in its original language accompanied by a literal (word-for-word) translation in which each line of translation is placed directly underneath that of the original.
Latin
Commentaries on the Gallic War, by Julius Caesar (Google Books, pdf) [very detailed book I]
Commentaries on the Gallic War, by Julius Caesar (Google Books, pdf) [books I through VII]
Epitome Historiae Sacrae, by Andrew Cornstock (Google Books, pdf)
The Metamorphoses, by Ovid (Google Books, pdf) [book I]
Selections from the Metamorphoses and Heroides, by Ovid (Google Books, pdf)
Agricola and Germania, by Tacitus (Google Books, pdf)
Selections from the History of Rome, by Livy (Google Books, pdf)
Cornelius Nepos, by Cornelius Nepos (Google Books, pdf) [interlinear text begins on page cxv and 116 respectively]
The Fables of Aesop, by Aesopus (Google Books, pdf) [interlinear text begins on page 79 and 94 respectively]
Opera, by Sallust (Google Books, pdf)
The Works of P. Virgilus Maro, by Virgil (Google Books, pdf) [the Bucolics, the Georgics, and the Aeneid]
Greek
The Anabasis of Xenophon, by Xenophon (Google Books, pdf)
Selections from Lucian's Dialogues, by Lucian (Google Books, pdf)
The Iliad, by Homer (Google Books, pdf)
Selections from Herodotus's Histories, by Herodotus (Google Books, pdf)
Latin
Commentaries on the Gallic War, by Julius Caesar (Google Books, pdf) [very detailed book I]
Commentaries on the Gallic War, by Julius Caesar (Google Books, pdf) [books I through VII]
Epitome Historiae Sacrae, by Andrew Cornstock (Google Books, pdf)
The Metamorphoses, by Ovid (Google Books, pdf) [book I]
Selections from the Metamorphoses and Heroides, by Ovid (Google Books, pdf)
Agricola and Germania, by Tacitus (Google Books, pdf)
Selections from the History of Rome, by Livy (Google Books, pdf)
Cornelius Nepos, by Cornelius Nepos (Google Books, pdf) [interlinear text begins on page cxv and 116 respectively]
The Fables of Aesop, by Aesopus (Google Books, pdf) [interlinear text begins on page 79 and 94 respectively]
Opera, by Sallust (Google Books, pdf)
The Works of P. Virgilus Maro, by Virgil (Google Books, pdf) [the Bucolics, the Georgics, and the Aeneid]
Greek
The Anabasis of Xenophon, by Xenophon (Google Books, pdf)
Selections from Lucian's Dialogues, by Lucian (Google Books, pdf)
The Iliad, by Homer (Google Books, pdf)
Selections from Herodotus's Histories, by Herodotus (Google Books, pdf)