The books category has coupons for general bookstores, textbook merchants, and online malls that also sell books.
Barnes and Nobles has most books currently published. They also offer a selection of calendars, gifts, reading accessories, and magazines. Every month new coupons come in, in addition to the free shipping offers that are usually available.
There are several merchants that sell textbooks. These books are already significantly discounted compared to campus bookstores.
Phat Campus offers textbooks that are significantly discounted - if you use one of their free shipping coupons you can make considerable savings over the campus bookstore. Wiley publishes many science, math, and engineering texts and offers discounts when you purchase directly from them.
Alibris offers lots of coupon codes very reliably at the beginning of each academic semester. In addition to the books, textbooks, music, and movies that are available from most media merchants. In addition to this, Alibris also offers a selection of rare and collectible books.
a1Books offers decent 5%-10% off discounts on fiction, non-fiction, and textbooks.
The Scholastic Store frequently offers sales worth up to 75% off particular categories.
HCI Books offers a wide range of books on self-help, fitness, mental health, and addiction and recovery.