J. Gresham Machen

Need a good read? Not much money? Want something out of copyright, but in relatively modern English? Has it got to be relevant, intellectually challenging, yet able to stand the test of time? I've just started "Christianity and Liberalism" by J Gresham Machen. I'd recommend it to anyone, Christian or not Christian, wanting to understand Christianity, the Church today or the nature of religion over and against secularism. And I've only started reading! What are you reading?