The internet classics archive, an incredibly useful resource.
The text of Plutarch's Lives is here in its entirety, and the site has an excellent search engine that can shave hours off of writing papers. Plutarch's biography of Antony was Shakespeare's main source of the play, and comparisons can provide valuable insight.
Joyce Carol Oates' essay on the play.
http://www.usfca.edu/fac-staff/southerr/antony.html
Among other things, Oates explores the play's relationship with the form of tragedy.
