Introduction to The Tempest. This is the Penguin Classics' introduction to its edition of The Tempest. The discussion here is good, and the middle of the page contains a fine plot summary of the play, as I promised you. Of course, as you can guess, if I'm giving this to you, it must not be sufficient to get you through the course without reading the play itself. Then again, neither is the Cliffs Notes version, so read the play, and you'll find much to enjoy! This summary is a good way to get an overview of the plot, and consulting it at various points in your reading can be a helpful way of keeping track of the action.
Introduction to French Renaissance theater.
Background on the Trojan war
Carlos Parada's Greek Mythology site.This is a great source of information on characters in Greek mythology (scroll down for list).