How did I not post this earlier? Christian Audio - one free audiobook a month. Usually they're not great books, but I did get Piper's Desiring God back in and that was a heck of a book. There's plenty more interesting stuff, but most of it costs money.
BOY OH BOY. Simply by listening to these guys discussing antinomianism, I've gained a new respect for the Reformed tradition and a greater sense of how little I know. And I've just found audio of Calvin's Institutes.