1. Book Gorilla- This one is my favorite. They send me a full list every morning of at least 10 or more books that are either free or low price. You can even receive a list of up to 50 books! You choose. They are specific to Kindle though.
2. Book Bub- BookBub alerts you to limited-time free & discounted ebooks.
It's free to join, you can read on any device, and the books are yours to own. I picked my favorite genres and every morning I get an email listing several books. I only get about 4 or 5 books though, so the variety is semi limited.
3. Books that Buzz- I found this one because it is an author resource where books are listed and promoted. However, because I subscribe, every day I get a list of discounted ebooks and book giveaways. Love it! This service also sends me about 10 books a day.