Massachusetts Institute of Technology
Mit: Internet Classics Archive: Protagoras
This site from the Internet Classics Archive provides the full text of Plato's dialogue, "Protagoras." Translation by Benjamin Jowett.
Other
The Sophists and Socrates
Wonderful essay on Socrates refutation of the Sophists. Discusses Socrates' debate with Protagoras over the meaning of "arete" (justice) and its consequences for the democratic politics of Athens.
Internet Encyclopedia of Philosophy
Internet Encyclopedia of Philosophy: Protagoras
Good introduction from the Internet Encyclopedia of Philosophy to Protagoras and his significance within ancient philosophy.