research help for ENGL 215 students
First of all, see the "Research" section of this page.
The Ancient World
In studying classical literature, you will not find a great deal of helpful material online. There are of course exceptions, but as a rule, online sources will do little more than offer you a basic orientation to your subject: if you want to do serious research you'll have to explore scholarly journals — those on campus and online should try the vast scholarly archives of JSTOR and Project Muse — and scholarly books. Don't forget to consult the bibliographies and introductions in the editions I have assigned you: they will give you better advice than I can provide.
But for that basic orientation, you could check out the Encyclopedia Mythica, which has sections on Greek and Roman mythology — though in many cases, Wikipedia works just as well or better. Again, let me emphasize that you shouldn't be citing these sources, just consulting them for general information.
More ambitious and valuable, though perhaps less user-friendly, is the vast Perseus Project at Tufts University. It contains thousands of pages of texts, in the original languages and in translation, from ancient literature, philosophy, and history. There's even a substantial collection of serious scholarly work that's in the public domain. Much of this is seriously out of date, but it can be worth consulting all the same. The Bryn Mawr Classical Review is a serious scholarly journal that appears only online. Its articles are typically on recent scholarship and so might not be directly helpful to you, but they can alert you to work that you'd benefit from reading.
The Middle Ages
The Orb is a useful online encyclopedia of medieval culture — a good place to start, unless you wish to begin with beauty rather than utility, in which case you might want to take a look at these images of medieval manuscripts from Oxford University. Or perhaps the online gallery of the British Library.
But I'd probably begin with a subset of The Orb, the amazingly detailed Internet Medieval Sourcebook, or with a similar site that will lead you to many of the same sources, The Labyrinth. Orbs or labyrinths, it's up to you. Oh, and Jack Lynch's guide is really good too.
Writings from the early centuries of Christianity are immensely important for understanding the medieval world, and a linked list of the best online resources may be found here.
The Early Modern Period
I hope to add more links later, but for now, please know that there is an enormous collection of references at the Voice of the Shuttle's page on Renaissance and Seventeenth Century Literature. Also see the British Academy's portal to sites devoted to the early modern period. And due honor should be paid to the titanic efforts of Anniina Jokinen to build her vast site called Luminarium.