Kobo have several very generous coupons right now:
Welcome75us – 75% OFF expires today
Welcome75ca- expires today
AND  Welcome90us- 90 (!) %OFF  expires… sometime.
         Welcome90ca
Welcome10us- 10 dollar discount ( The book has to cost at least 10 dollar for it to work)
Welcome10ca

Welcome5us – 5 dollar discount
Welcome5ca 

Welcome50us- 50 percent off (!).
Welcome50ca

I have used them all, and saved lots.  At least 50 dollar.  Edit: I counted, and I have bought 80 dollars worth of books, and paid less than 30 dollar for them.  (I aimed for the 15 dollar plus e-books for the big discounts, and used 10 dollar off on books that cost 11 dollar. )

  Johanna Lindsey’s backlist is on sale for 3.99.

For paper readers, The Bookdepository offers an additional 10% off.  Add APMA12 during checkout.