This year's Free RPGDay release James Edward Raggi IV's Eldritch Cock is now available for the glory of all at the great price of pay-what-you want. You can read my review here.
Kelvin Green's extremely limited print run book Fish Fuckers is also available in pdf form. At 7.99 it's a great price. I love the adventure and you can read my review here. Don't let the title keep you away. Yes there is fish man fucking involved, but it's actually a rather clever adventure.