Ancient Skepticism 
From the Stanford Encyclopedia of Philosophy, by Leo Groarke. Article on the two movements in ancient philosophy, Pyrrhonism, and Academic Skepticism.
http://plato.stanford.edu/entries/skepticism-ancient/Classical Skepticism: Issues and Problems
By Peter Suber of Earlham College
http://www.earlham.edu/~peters/writing/skept.htm
Ancient Scepticism and the Contra Academicos of St. Augustine
A paper by Bernard Wills closely examines the logic of Augustine's response to ancient scepticism in his Contra Academicos.
http://www.mun.ca/animus/1999vol4/wills4.htm
Ancient Greek Skepticism
An article on skepticism in Ancient Greece from the Internet Encyclopedia of Philosophy, by Harald Thorsrud of Temple University.
http://www.iep.utm.edu/s/skepanci.htm
