The Euthydemus is a Socratic dialogue pitting Socrates against two brothers, the sophists Euthydemus and Dionysodorus.
Free Online Texts
Gutenberg: Euthydemus by Plato, translated by Benjamin Jowett, multiple formats.
Internet Classics Archive: Euthydemus, translated by Benjamin Jowett, online text.
University of Adelaide (Internet Archive): Euthydemus, translated by Benjamin Jowett. EPUB, HTML and MOBI formats.
Wikisource: Euthydemus, translated by Benjamin Jowett. Online text, downloadable via bookcreator.
Approaching Plato: A Guide to the Early and Middle Dialogues
History of Philosophy without any gaps: Know Thyself: Two Unloved Platonic Dialogues - podcast with philosophers Peter Adamson and M.M. McCabe.
Librivox: Euthydemus - audiobook.
PhilPapers: Plato - Euthydemus - bibliography with open source option.
The Great Conversation: Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: Plato's Dialogues are listed.