The Sophistical Refutations (Greek: Σοφιστικοὶ Ἔλεγχοι; Latin: De Sophisticis Elenchis) is the final work of the Organon, the traditional collection of Aristotle's logical writings. Like the preceding Topics, its subject matter concerns aspects of logic that are significant for the art of rhetoric, in this case, the identification of fallacies.
Free online texts
Loebulus. L400 - Aristotle -- On Sophistical Refutations. On Coming-to-be and Passing Away. On the Cosmos. PDF of public domain Loeb edition in Greek and English.
Poesia Latina: Sophistical Elenchi - Greek text, HTML format.
University of Adelaide (Internet Archive): On Sophistical Refutations. Multiple formats.
Wikisource: The Sophistical Elenchi, translated by O.F. Owen. Multiple formats.
ChangingMinds.org: Aristotle's 13 Fallacies.
History of Philosophy without any gaps: Aristotle's Logical Works - podcast by philosopher Peter Adamson.
Internet Encyclopedia of Philosophy: Aristotle: Logic, by Louis F. Groarke.
Librivox: Sophistical Elenchi - public domain audiobook.
Stanford Encyclopedia of Philosophy: Aristotle's Logic, by Robin Smith.
Wikipedia: Sophistical Refutations.
Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.