Humble Bundle is an interesting website where publishers allow certain materials to be bought in discounted bundles, sharing the revenue with various charities. At this time (For the next two weeks, approximately) there is a bundle of Tolkien-related books available. For as little as $18 you can get 27 books (more, or less, Tolkien-related). The titles in this bundle are available in DRM-free PDF and ePub formats so you can read them on just about any computer, phone, tablet or eBook reader.

This is an excellent chance to get some digital titles from the likes of Shippey and Garth, if nothing else!

https://www.humblebundle.com/books/all-about-tolkien-books

The titles in the full bundle are:
  • J.R.R. Tolkien: Author of the Century, by Tom Shippey
  • Mythmaker: The Life of J.R.R. Tolkien, by Anne E. Niemark
  • The Road to Middle-Earth, by Tom Shippey
  • The Wizard's Dessert Cookbook, by Aurelia Beaupommier
  • Tolkien's Art, by Jane Chance
  • Defending Middle-Earth, by Patrick Curry
  • Ents, Elves, and Eriador, by Matthew Dickerson and Jonathan Evans
  • Breaking the Magic Spell, by Jack Zipes
  • Tolkien and the Great War, by John Garth
  • Famous, 1914-1918 (Includes chapter on Tolkien), by Richard Van Emden and Victor Piuk
  • The Well at the World's End, by William Morris
  • Walking English, by David Crystal
  • War in Heaven, by Charles Williams
  • All Hallows' Eve, by Charles Williams
  • Descent into Hell, by Charles Williams
  • Many Dimensions, by Charles Williams
  • Shadows of Ecstasy, by Charles Williams
  • The Ballad of the White Horse, by G.K. Chesterson
  • The Beasts of Valhalla, by George C. Chesbro
  • The Book of English Magic, by Philip Carr-Gomm and Richard Heygate
  • The Greater Trumps, by Charles Williams
  • The Place of the Lion, by Charles Williams
  • The Tao of Travel, by Paul Theroux
  • We Install, by Harry Turtledove
  • She, by H. Rider Haggard
  • Beowulf, translated by J. Lesslie Hall
  • Fifty-One Tales, by Lord Dunsany

https://www.humblebundle.com/books/all-about-tolkien-books