From Frog God Games:
Frog God Games has discounted their entire line of Swords & Wizardry products for 1 day only in celebration of Swords & Wizardry appreciation day (April 17th 2013). The discount is good for 25% off S&W Products but you must use coupon* code SWApprDay on April 17th 2013 at check out.
*The coupon excludes items less than $1, S&W Cards, Pre-Orders, and Subscriptions.
From the Swords & Wizardry SRD site:
Here is the coupon code for the Swords & Wizardry Appreciation Day sale [17 April 2013]!
It applies to everything listed here: http://shop.d20pfsrd.com/collections/swords-wizardry-appreciation-day
Happy S&W Appreciation Day!