While new English translations of Plato's writings continue to be published, older translations are no longer copyrighted and are available on-line. Due to space limitations, I was only able to anthologize excerpts from Plato's works, but here are the links to the full sources, as well as resources for teaching and interpreting the texts.
The complete text of Plato's Republic (with commentary, and in both English translation and original Greek) is available on the Perseus Digital library (where you can also access many other ancient texts).
The full text of Plato's Crito(translated by Benjamin Jowett) is available on the MIT Internet Classics Archive.
If we want to understand Socrates' views of his relationship to the city, then it is also important to read Plato's Apology. The full text, translated by Benjamin Jowett, is available on the MIT Internet Classics Archive. In fact, all of Plato's works can be found on this site.