Wool: The Graphic Novel Omnibus from Jet City is on sale again until 1/17/16. It's from Palmiotti and Gray, so it has to be good.
https://www.comixology.com/Wool-Sale/page/9426
From Image until 1/18/16, a Michael Moreci sale (Roche Limit, Hoax Hunters, and Hack/Slash). Six $3.99/$4.99 collections and thirty $.99 singles. Remember with Image, usually, the single issues have more material than the collections.
https://www.comixology.com/Roche-Limit-Sale/page/9424
From Archaia until 1/19/16, a sale on four volumes of Spera, $5.99 instead of $12.99 each.
https://www.comixology.com/Spera-Sale/page/9425