The Theban Plays is a term often used for three tragedies by Sophocles; Oedipus the King, Oedipus at Colonus and Antigone; all of which deal with the legendary matter of Thebes and its King Oedipus. Although often regarded as a trilogy, the plays were not originally intended as such, being written at widely different times, as part of sequences now lost, and featuring different, sometimes incompatible, versions of the underling myth.
Free online texts
Gutenberg: Plays of Sophocles: Oedipus the King; Oedipus at Colonus; Antigone; translated by Francis Storr.
Internet Archive: Sophocles - Oedipus Tyrannus, Oedipus at Colonus, Antigone, translated by John Swinnerton Phillimore (1902). Multiple formats.
Internet Archive: Three Theban plays : Antigone, Oedipus the King, Oedipus at Colonus, translated by Theodore Howard Banks (1956). Multiple formats.
Loebulus. L020 - Sophocles -- Sophocles I: Oedipus the King. Oedipus at Colonus. Antigone. PDF of public domain Loeb edition in Greek and English.
University of Adelaide (Internet Archive): The Oedipus Trilogy (Oedipus the King - Oedipus at Colonus - Antigone), translated by F. Storr. Multiple formats.
Wikisource: Sophocles. Multiple translations.
Performances and Reviews
Theatre 80, New York
New York Times: Three Plays, Eight Actors, All Sophocles, by Rachel Saltz, 2 November 2008.
Peter J. Ahrensdorf translation
Davidson.EDU: Prof Offers Unadorned Translation of Sophocles Plays, 10 April 2014.
Notre Dame Philosophical Reviews: Greek Tragedy and Political Philosophy, reviewed by Edith Hall.
Sophocles' Three Theban Plays, resources by translator Jamey Hecht.
Youtube: Sophocles' Theban Plays, video blog by Phillip Zapkin.
The Great Conversation: Further reading at Tom's Learning Notes
Aeschylus: Seven Against Thebes.
Aeschylus: The Oresteia - the only true trilogy still extent from ancient Greek tragedy.
Aristotle: The Poetics.
A.E. Haigh: The Tragic Drama of the Greeks (1896).
Ancient Greek resources: Learn to read Greek classics in the original.