The Apostolic Fathers: A New Translation and Commentary, Volume 3: “Barnabas and the Didache” by Robert A. Kraft
This volume, originally published in 1965, was later relased online with updates by the author.
The translation of Barnabas with footnotes but without commentary is available here as:
The full text of the book with translation and commentary is available at http://ccat.sas.upenn.edu/rak/publics/barn/barndidintro.htm.