Comixology will be tweeting codes for free books all weekend possibly. First two are COLLIDE and UNITY. Enter them in the redeem section of Comixology for the freebies to automatically be added to your account.
https://www.comixology.com/redeem
I doubt I'll return to post them each hour or whatever, so follow Comixology if you want free comics.
Also, the Dark Horse weekend sale is 59 books by the great Mike Mignola.
https://digital.darkhorse.com/genre/206/