Who needs 50 lb, 20-volume Bible commentaries when you have this Web site? Check out Christian Classics Ethereal Library (http://www.ccel.org/)—a Calvin College labor-of-love.
Probably the coolest thing I ran into in my brief initial visit is the world-wide study Bible, which has links to study resources for each verse of the Bible: multiple translations, audio, dozens of different commentaries, sermons… And it has these on verse, chapter and book levels.
But if you’re working for the works of Augustine, Luther, Justin Martyr… they’re here.
The amount of information available, not just here, but everywhere, to the would-be disciple of Christ, is just staggering.