Cosmos of the Ancients: Prodicus of Ceos: Concise article on this thinker, by Stefan Stenudd.
Internet Encyclopedia of Philosophy: Prodicus: Short article on this leading Sophist.
Plato and His Dialogues: Prodicus of Ceos: A resource provided by the Perseus Project, with links to every mention of this Sophist in Plato's dialogues.
Wikipedia: Prodicus: Article incorporating information from the 1911 Encyclopaedia Britannica.