Approaching Plato: A Guide to the Early and Middle Dialogues by Mark Anderson and Ginger Osborn,
an online text designed to provide aids to the study of Plato‟s early and middle dialogues. Here you will find material covering 15 of Plato‟s works. For each of the dialogues there is a list and brief description of the main characters, outlines (both a short and a longer, more detailed version), and an interpretive essay. Other supplementary material is included as well, such as an imagined letter from Xanthippe to her mother reflecting on the actions of Socrates and his friends during the days leading up to the philosopher‟s execution; and an account of the various ways Socrates characterizes his relation to the oracle of Apollo in the Apology. The longer outlines are supplemented with Greek text so that those who know the language can see for themselves the original words and phrases behind our translations.
We have designed the material included on this site to be of use to students and professors of every level.
History of Philosphy without any gaps by Peter Adamson, Professor of Ancient and Medieval Philosophy at King's College London. While the podcasts cover more than just Plato, there are already several on Plato with a new podcast added each week. The list of episodes might be the fastest way to find the topic you want.
The Stanford Encyclopedia of Philosophy appears to have several entries covering Plato, as does the Internet Encyclopedia of Philosophy.
I'll mention The Leo Strauss Center again as they continue to add to their collection of tapes and transcripts of various Strauss' courses.
Open Culture lists several courses available under the "Philosophy" and "Classics & Classical World" sections that cover Plato. A search at their home page will turn up more resources.