calibre - Ebook manager, viewer & converter
AbeBooks - AbeBooks has millions of new & used books, rare books and out of print books.
Apple Books - The all-new Apple Books has been redesigned to make finding, reading, and listening to books a beautiful, effortless experience on iPhone and iPad.
DealOz.com - Save time. Save money. Discover. Search new and used books, textbooks, and ebooks using the most trusted shopping comparison site, DealOz.com.
Open Library - The ultimate goal of the Open Library is to make all the published works of humankind available to...
Occupy the Bookstore - Chrome extension to easily surface cheaper textbooks