Here is a summary of all the offers I have spotted until now (to be regularly updated):
Chaosium — use the code BLACKFRI23 at check-out and get 10% off your order on chaosium.com
Mindjammer Press — 30% off all their digital products at DriveThruRPG
Lamentations of the Flame Princess — 25% off all their PDFs at DriveThruRPG
Lots of Jonstown Compendium items are discounted.
LULU — use the code TWINKLE30 and get 30% off all print orders.