It isn't exactly a sale, but I've found CCG Armory very useful and the cheapest on the web for items that you can't find discounted otherwise. They don't have the selection or used product that Troll & Toad, Noble Knight, or FRPGames have, but they're a good place to buy new RPGs that aren't being discounted elsewhere.
For instance, I recently purchased Mordenkainen's Magnificient Emporium for $19.50 (list $30) and Designers & Dragons for $34.50 (list $50), when those books can't be found for much less than list price even on Amazon. Plus, shipping was only $4 per book (I ordered them at different times) - and media mail was fast, less than a week.
I've heard occasional grumblings about CCG Armory but I've ordered from them a half dozen times and never had anything but a good experience.