Barnes & Noble (nook):
Page Foundry (inktera):
tolino: (I don't have a link for this one.)
24symbols: (Should be available soon.)
P.S. In addition to the above, there are the following editions of the
book. These options have different prices, shipping times, shipping
costs, customs and other fees, availability at local book stores, etc.
978-0-692-59943-3 hardcover by IngramSpark (will be available in a week
or two): The most expensive print option; can be available at your local
store but you may have to pre-order.
978-0-692-52957-7 paperback by IngramSpark: Less expensive print option;
can be availableat your local store but you may have to pre-order.
978-1-515-07460-1 paperback by CreateSpace: The least expensive print
option; not available in local stores.
Pay-what-you-want ebooks at Gumroad: https://gum.co/PinD
Free HTML, PDF, EPUB, AZW3, and MOBI at http://ddili.org/ders/d.en/