The 2 x 40% off discount codes we've had access to since November sometime (?), bargainmoose40 and vouchercodes40 are going to be sorely missed by this buyer.
Kobo's got purchases from me that I otherwise wouldn't have made - not just from Kobo, but in ebook format at all.
Also, whilst I have no evidence to support this, I suspect that Amazon and Books on Board have been price matching to coincide with the codes. Maybe not all titles/authors all the time, but certainly some of the time.
Maybe a last minute look see at what 40% off can get me is in order!!