Mark Twain's assault on Christianity
I don't know how many people have read this, but the great American author Mark Twain grew to be a vehement atheist in his old age. He wrote "Letter's from the Earth", a great polemic-style deconstruction of Christian mythology. The entirety is available here.
http://www.positiveatheism.org/hist/twainlfe.htm
I especially like this because it argues purely from the bible's own logic and story, rather than basing it on scientific grounds. He focuses on analyzing the implications of the bible rather than if it is literally true, which I feel represents a possibly higher form of critique.