Here are some of the sites I’ve found that will promote 99c sale ebooks (and often sale books up to $2.99, as long as the books are deeply discounted). Most of them are ones I use myself. I’ve left out a number of sites that have no information on followers or subscribers, as well as those that tend to get bad marks from the indie writers on KBoards. Even so, that’s no guarantee that all of these sites will be effective. I suspect a lot has to do with genre, since sites that work for me get panned by other writers, while sites other writers swear by have been a washout for me. So remember, YMMV.
Bargain Booksy (Free and paid)
Reading Deals – Books should be a minimum of 50 pages long and have at least 5 reviews and a 4 star average. They also have the option to pay $29 for a guaranteed listing
Choosy Bookworm – Guaranteed listings start at $25. (My results with a paid listing were disappointing, but people report good results with their free slots.)
Awesome Gang – Also offer a featured 2 day listing for $10.
The Naughty List – For romance and erotica
EBookStage – Must have at least 5 reviews and a rating of 4 or higher. Require a number cross promotions for which you receive points. If you don’t have enough points for a free promo, you can pay for a slot. Prices start at $10.
Book Angel – Book must be PG-13! Only for books under 1 British Pound that are available in the UK store.
Read Cheaply – Prices start at $25, depending on genre. Note: Do not try to book an ad with them if you’ve had a book listed within the last month. http://readcheaply.com/partners/
Bknights on Fiverr – https://www.fiverr.com/bknights/
Book Barbarian – Prices starting at $20. Requires at least 10 reviews and a rating of at least 3.5. Only for science fiction and fantasy. Usually necessary to book at least a month in advance. One book per author within a 30 day period. http://bookbarbarian.com/ad-requirements/
Bookbub – This is the heavy hitter in paid advertising; it is also Very Expensive. https://www.bookbub.com/partners/pricing
Ereader News Today (ENT) – Prices starting at $30. http://ereadernewstoday.com/pricing/
ManyBooks.net – Prices starting at $25. Requires at least 10 reviews and an average of 4 or higher. My results here used to be quite good, but recently they have been disappointing, especially given the price. http://manybooks.net/promote.php
Booksends – Requires at least 5 reviews, with a high overall average, and an attractive cover, with a planned sale price of less than $3 and at least 50% off full price. Prices start at $10 and increase according to sale price and genre. Through this site, it is also possible to advertise with EReaderIQ. http://booksends.com/advertise.php
eReaderiQ – It is also possible to book eReaderiQ separately. Prices starting at $5. http://www.ereaderiq.com/authors/submissions/dds/
Buck Books – For 99c sale books. Books must be at least 60 pages long, and have at least 10 reviews with an average of 3.8 or higher. Prices start at $9 for fiction.
BookGorilla – Prices starting at $40 depending on genre and price. Usually necessary to book at least 6 weeks in advance. http://www.bookgorilla.com/advertise
Books Butterfly – Various pricing options starting at $50, depending on how many readers you want to reach. http://www.booksbutterfly.com/order/paidbookslots/
Robin Reads – $40. http://robinreads.com/author-signup/
ContentMo – Various promo plans starting at $1.99 a day. http://contentmo.com/99-book-promo-2015/
Ebookhounds – $10 for a listing. Extra options available as well.
The Fussy Librarian – Promotional options starting at $8, depending on genre. Books must have at least 10 reviews and a 4.0 rating, except for new releases. http://www.thefussylibrarian.com/for-authors/
Sweet Free Books – $7. At least 5 reviews and a 3.5 rating. http://sweetfreebooks.com/advertise/
FreebooksHub.com – Promotions starting at $10.
Kindle Books and Tips – Prices starting at $25. Books must have at least 8 reviews, at least 4 of which must be Amazon Verified Purchase reviews. No short stories. http://www.fkbooksandtips.com/for-authors
Digital Book Today – Offers a variety of advertising options, some of which are free. http://digitalbooktoday.com/join-our-team/paid-and-free-promotions/
Free & Discounted Books – Promotion for eBooks from 0.99-2.99 starting at $8. http://freediscountedbooks.com/99-cent-sales/
Hot Zippy – Various promo plans starting at $23. http://hotzippy.net/feature-your-book.html
Ebook Soda – Prices starting at $15. Kboards authors report that it isn’t particularly effective. http://www.ebooksoda.com/
Bargain Booksy – Prices for an ad start at $25 and depend on the genre. http://bargainbooksy.com/sell-more-books/
Book Goodies – $10 to promote a Countdown Deal.
eBook Betty – Listings with various review criteria starting at $18 http://bettybookfreak.com/authors/
It is also possible to list your book on a number of Facebook groups specifically for 99c eBooks, usually while it is on sale:
Author 99cent Book Promotions: https://www.facebook.com/groups/444695995585913/
Addicted to eBooks: https://www.facebook.com/pages/Addicted-to-eBookscom/277297772316389
EReader1-US: https://www.facebook.com/eReader1.US/ Instructions are here: https://www.facebook.com/notes/ereader1-us/book-promotions-including-self-promo-by-authors-and-publishers-and-their-friends/448662358501661
If you know of other effective sites for promoting a 99c sale, please let me know in the comments!