Go to Winterhold, start heading up the path as if you're going to do the dragon bounty for the jarl, you will come to a cave called the "Sightless Cavern". Continue past it up and around a corner, you will come to an alter with skeletons. Next to the alter there are Boots and a Shield. Picking them up will make the skeletons come alive. After killing them, the skeleton that was on the alter will have a "Book of Oblivion" in his inventory. This book will never disappear. Continue looting the body for an infinite number of books worth 50 gold each.