Context for the Evidence: Antiphon
A brief guide to this ancient thinker, by David D. Phillips. Published in The Stoa in 2003.
MacTutor History of Mathematics: Antiphon the Sop
Article on this ancient thinker or thinkers, with bibliography and cross-references.
The Internet Classics Archive: Works by Antiphon
Online texts of Antiphon's speeches, in Greek and English.
Wikipedia: Antiphon
Short entry incorporating material from the 1911 Britannica.