You need the stiff, supportive sorts of covers that hardbound books have, and then you incorporate rare earth magnets into the bottom part of the covers and make the shelf out of steel. So long as the magnetic attraction is enough to make it difficult to knock over a book, you should be in pretty good shape. Note that while it says "no end" it doesn't specify infinite, so if you make a shelf in the shape of a möbius strip, you can have a finite collection with no end. This shape shelf is especially helpful with a magnetic attachment scheme, since you can have the thinner books with the unmagnetized end being downward so that gravitation helps to keep them in their proper orientation.