Someone started, on this thread, a list of websites that have daily deals. Here's one that I don't think has been mentioned. Would be on Non-Publisher-Specific list; however, it is subject-specific--"Christian Interest."
Non-Publisher Specific.
Gospel eBooks. Seems like they consistently have the best deals of "Christian Interest" out there. There are a few "sponsored" ads on the site, but they're easy enough to ignore, if that's what you want to do. However, a lot of those books are free, and you occasionally can find a jewel among them. Another benefit of this website is that they have information that you just can't seem to find anywhere else--like the date that the sale on a book is scheduled to end. If I have time to check just one "Christian Interest" website on a day, this is definitely it. Note: all of their offerings are for
Kindles. I've read that they're easy to convert to ePub's; I have no experience with that, myself. Too, if one's on sale, and you don't want Kindle, you can try checking ChristianBook.com, GooglePlay, Kobo . . . . you know, all of the usual suspects.
I still hope to compile a master list of all of the websites with daily deals, and will probably start a non-sticky thread just for making additions to the list, if allowed by MobileRead rules.