The J. B. Lightfoot editions: These include Greek text, manuscript facsimiles, and translations.
Part I: S. Clement of Rome, Vol. I
Another copy.
Part I: S. Clement of Rome, Vol. II
Part II: S. Ignatius; S. Polycarp, Vol. I
Part II: S. Ignatius; S. Polycarp, Vol. II
Loeb Classical Library, with translations by Kirsopp Lake:
Vol. I: I Clement, II Clement, Ignatius, Polycarp, Didache, Barnabas
Another copy.
Better scan at the Internet Archive.
Vol. II: The Shepherd of Hermas, the Martyrdom of Polycarp, and the Epistle to Diognetus
Another copy.
Better scan at the Internet Archive.
Rev. George A. Jackson:
The Apostolic Fathers and the Apologists of the Second Century, 1879.
The same, 1884 edition, at archive.org.
William Wake’s 18th-century translations:
Genuine Epistles of the Apostolical Fathers
London, 1817
London, 1840
Philadelphia, Association of Gentlemen, 1846
Hartford, 1839 (with fine engraved frontispiece)
Temple Chevallier:
A translation of the Epistles of Clement: of Rome, Polycarp and Ignatius, and of the first apology of Justin Martyr, by the Rev. Temple Chevallier. New York, 1846.
James A. Kleist:
The Epistles of St. Clement of Rome and St. Ignatius of Antioch. Newly translated and annotated by James A Kleist. Westminster, Maryland: The Newman Bookshop, 1946.
Ante-Nicene Christian Library.
Volume I. Apostolic Fathers with Justin Martyr and Irenaeus. Apostolic Fathers: Clement, Ignatius, Polycarp, Barnabas, Hermas, Epistle to Diognetus, Papias, Justin Martyr, Irenaeus.
Didache.
The Didache or Teaching of the Twelve Apostles, restored to its original state from various sources, with an introduction, translation, and notes. By Charles H. Hoole, M.A. London, 1894. —An excellent scan with excellent OCR.
At Google Books.
The Oldest Church Manual, Called the Teaching of the Twelve Apostles. The Didache and kindred documents in the original, with translations and discussions of post-apostolic teaching, baptism, worship, and discipline, and with illustrations and fac-similes of the Jerusalem Manuscript. By Philip Schaff. Second edition, New York, 1886.
At Google Books.