If you have an interest in early English literature, don't miss Luminarium, a thoroughly and elegantly done web site on the subject with music to go with it, so when you pull up the page for a particular author, Christopher Marlowe for instance, you hear a two- or three-minute composition from the period, in this case a beautiful piece by John Dowland. Try it -- you'll never be the same.

Finally, these are Great Books web pages and general book sites of one kind or another: