For folks new to Kobo, who don't look at the main Kobo forum, there is a discount thread there that is updated when the new discount codes come out. There are a bunch of them that have been released today. Read the first post
to see how the discounts work, what books can be discounted, and then check in to see the current codes. The OP updates the first post, but when there are a bunch of new ones, it always pays to look at the end of the thread.