Smashwords' site continues to be terribad at organizing/showing the sale stuff. And I don't think I like their new cart.
Anyway, here's a few of the more notable participants this year. And it is rather a "few", considerably down from previous years.
Just like I did, you will have to dig through some fairly long listings just to see if some books you are interested might be free/on sale. Most are not.
Publishers/multi-author imprints:
Canadian backlist publisher
Bev Editions has nearly their entire catalogue either offered free-with-coupon or at significant sale prices. Mystery, literary fiction, historical non-fiction, etc. by authors such as Arthur Ellis Award-nominated mystery writer Lyn Hamilton, Stephen Leacock Memorial Medal winner Morley Torgev, etc. Recommended.
LGBT specialty publisher
Lethe Press (who've had books featured in those Weightless Books 1-day sales occasionally mentioned in the F&SF thread) only have one freebie this year,
a novella by Alex Jeffers, but they are offering 75% off a substantial selection of titles, including several sfnal anthologies based on LGBT takes on literary, mythological, and pop culture (including Dracula and Edgar Allan Poe), as well as more scholarly non-fiction, and several novels of various genres, including fantasy, historical, romance, and mystery (a set of sequels to one of last year's freebies is on sale, if you happened to read and enjoy the "Beach Reading" series).
The western & romance imprints
Western Trail Blazer and
Rebecca J. Vickery, which have a number of established backlist genre authors and which I suspect to be from the same company had quite a few freebies last year. This year, they seem to 50% off a very few selected titles in their very large catalogue, from the spot checks I did. There may be freebies among them. I didn't care enough to go through all the pages of their titles to see.
Booktaste/Darling Newspaper Press is one of the few former RAEBW participants to advertise RAEBW 2014 on their website, and they are offering a handful of Smashwords coupon freebies, mostly historical/adventure fiction. Scroll down to where it says "Great titles FREE for Read An Ebook Week" on their website frontpage to get direct links to all the eligible titles.
Individual authors whom I've checked:
Former Baen and Harlequin fantasy & paranormal romance author
Doranna Durgin is once again offering a few freebies, and 50%+ discounts on several of her previously Baen-published fantasy novels (some previously freebied in past years).
Gary K. Wolf, author of the books which the film
Who Framed Roger Rabbit? was adapted from, returns to once again offer those particular books free along with some others, and 50% discounts on some of his other titles, including a short story collection involving tales set in the Toontown universe of WFRR?, which I'll probably pick up.
Canadian Aurora Award-nominated sf/fantasy writer
Douglas Smith is offering 50% off selected works, including several anthologies of previously published short stories which I will likely be purchasing shortly once I confirm that I don't already own them through another source (at least one anthology of which was itself previously print-published by specialty imprint ChiZine). I think he also has a freebie short, but I'm not digging back to check.
Romantic Times Award-winner
Marsha Canham is offering two of her historical romances free with coupon, and one free to download, but does not otherwise look to have anything on special sale.
UK mystery & romance author
Marina Oliver, who has been published by imprints such as Robert Hale under quite a few pseudonyms, returns to offer 50%-75% off selected titles (mostly historical romance, though there are a few mysteries). Unfortunately, she has a very long listing of books and only a few on sale, so you'll have to dig quite a bit.
Other non-Smashwords participants this year:
Twilight Times Books are once again offering freebies direct to download on their website and are offering 50% off selected titles bought via Omnilit until RAEBW ends on the 8th. A mix of mystery, sfnal, and writing advice, mostly.
Fellow MR member publisher
Untreed Reads is offering 30% off much of their catalogue for RAEBW bought directly from their store.
That's pretty much it for this year, I think.
ETA: It may or may not be worth your time to seek out previous years' RAEBW threads for convenient linkage to genre authors who've offered things free/discounted in the past and might be doing so again.