Red Moon and EN Publishing have the $1 sales.
It looks like Creative Conclave, Living Imagination, and Silverthorne Games are 50% off .
Reality Deviant Publications looks like 50% to 75% off ($.50 for Order of Eudeus is crazy good)
Zeitgeist has significant discounts for blackmoor stuff (40%?)
Inner Circle has significant discounts on their Denizens and Isle Lorebooks (not sure of % but very high for the individual denizen ones).
WotC appears to be 35% off on current edition stuff (35% off normal cover print price).
I think the Le is around 35% off as well. (Some great deals there like on Pimp my Paladin, but avoid the normally $.50 unorthodox orthodox that is now on sale for $150.00)
Adamant has 30% off as do Dreamscarred Press I believe.
AEG, White Wolf, Bastion/DragonWing, Malhavoc, Mongoose, Highmoon Media(Monkeygod) Bards and Sages and others are doing 25% off. (White Wolf recently made scarred lands stuff either $10 or $5 so a lot of great deals to be had, though mostly for scanned image pdfs).