Here are some additions to bgalbrecht's excellent list of places on the web which send out lists of deals on a regular basis. The links are to webpages where you can subscribe to the lists.
Not Publisher-Specific.
Bargain Booksy. Oddly, the selection of ebooks in the page that they send you may not seem very desirable. But follow the link near the top of the page or near the bottom of the page, to all of their bargain books, and I think that you will be much more pleased.
Books Butterfly. The name and number of email messages that you get depends upon which one(s) and how many of them that you sign up for. They all appear in the "to" area of your inbox, in this format: "Free Kindle . . ., "Free Apple . . .," etc.
They include the U.K. and Canada.
The Fussy Librarian. [I've had experience with a few of them. Fussy librarians, I mean, G].
Early Bird Books. To subscribe, click on the "subscribe" link in the extreme top righthand corner; a popup should appear, in which you can plug in your information in order to get on their mailing list.
Publisher-Specific.
Macmillan. When you finish checking the first page, click on the "here" link near the bottom of that page, and you will see many more deals.
Endeavor Media.
Chronicle Books. Their specials are good for a calendar month; but what they lack in frequency, they make up in discount. I saw price points of $0.99, $1.99, and $2.99, in this month's list, and noticed one ebook with a $30 retail price. To score even more great deals, click on "shop all deals," near the top of the first emailed page. I have a highly favorable impression of the quality of Chronicle's ebooks.
Ebook Extra. It's easy to overlook their emails because the name is so prosaic. Tyndale Publishing Company is behind those email messages. To squeeze the most deals out of their mailings, be sure to click on the yellow banner at the bottom of the first page of the email message.
More Later . . . .