The Dialogues of Plato translated into English with Analyses and Introductions by B. Jowett, M.A. in Five Volumes. 3rd edition revised and corrected (Oxford University Press, 1892). http://oll.libertyfund.org/titles/166,
A 5 volume edition of Plato by the great English Victorian Greek scholar, Benjamin Jowett. The scholarly apparatus is immense and detailed. The online version preserves the marginal comments of the printed edition and has links to all the notes and comments provided by Jowett.
The text is in the public domain.