Being able to take full advantage of e-books can be challenging, especially when they are on different platforms, have unique features and look completely different on-screen. However, when one can read the original text written by the Venerable Bede, or Aristotle's Metaphysics (or Tactus or Virgil and so on), the advantages of e-books make the challenges seem insignificant by comparison. Here are four of the most exciting collections you must know about.