Recommended reading - Christianity:
Dan Barker - Godless (2008)
Barker launches an extremely thorough critique of the Bible, addressing the myriad of contradictions and inconsistencies, the historicity of the Biblical Jesus, and the absurdity and improbability of many Biblical claims such as the resurrection.
Bart Ehrman - Jesus Interrupted (2010)
Ehrman carefully reviews and assesses the New Testament with a detailed and extremely thorough analysis of the figure we call Jesus. It shows objectively how the entire Jesus myth and indeed, all of Christianity is a purposely-designed fabrication rife with contradictions, inaccuracies, and sometimes outright falsehoods.
John Loftus - Why I Became an Atheist (2008)
Loftus attacks the full span of Christianity, addressing the philosophical arguments against theism, the historical incompatibilities and inaccuracies of the Bible, and the contradictions between creationism and modern science, and throughout it all is an undercurrent of personal experience as Loftus explains his own deconversion from devout evangelicalism to enraged atheist.
Recommended reading - Atheism:
Michael Martin - Atheism: A Philosophical Justification (1989)
Martin attempts a two-pronged defense of atheism: first by attacking theistic arguments regarding the implausibility of morality and purpose without God, second by defending against attacks specifically on atheism.
Erik J. Wielenberg - Value and Virtue in a Godless Universe (2005)
Wielenberg challenges the claims of theistic morality, next he advances naturalistic ethics and displays how theological justification is unnecessary for a good and moral life.
Richard Carrier - Sense and Goodness Without God (2005)
Carrier continues the trend of expanding metaphysical naturalism, but this is a more complex and thorough work covering the full spectrum of a developed worldview, addressing nearly every topic beyond just morality. Easy to understand and comprehensive.