: Still the undisputed heavyweight, Amazon accounts for over 50% of print book sales and 80% of ebooks. Its "Look Inside" feature remains a fan favorite for vetting books before buying.

: If you’re looking for classics and don't mind digital, this is the gold standard for free, legal ebooks that are in the public domain. Reader Perspectives

: A subsidiary of Amazon that operates as a global marketplace for independent sellers, making it the premier spot for rare finds and antique editions .