http://www.perseus.tufts.edu/hopper/collection?collection=Perseus:collection:Greco-Roman
This is an extensive database of ancient literature from Tufts University. It includes two annotated translations of Prometheus Bound.
Ancient History Encyclopedia
https://www.ancient.eu/Prometheus_Bound/
This is the Ancient History Encyclopedia's page for Prometheus Bound. It includes a detailed overview of the play, as well as links to related information on ancient theatre.
Encyclopedia Mythica
This is an internet encyclopedia that gives background on mythological figures featured in Aeschylus' play.