There have been a number of polemical anti-religion atheist books that have come out recently and in the last couple of years. They tend to be somewhat polarizing, and tend to turn off religious moderates. The book I just finished says that God ain't out there, but it isn't really one of them.
In God: The Failed Hypothesis. How Science Shows that God Does Not Exist physicist Victor Stenger in a very straight forward fashion explains chapter by chapter that God - as most commonly defined in the Judeo-Christian-Islamic tradition - is proven to not exist because the empirical evidence that should be present were such a God to exist is not present, and in other instances empirical evidence refutes claims of God's existence (e.g. the universe is approximately 13.5 billion years old, therefore a God that created the universe in 6 days 6000 years ago does not exist.)
Along the way, Stenger very briefly touches on some of the philosophical arguments against God's existence, but mostly he concentrates on writing about how the God concept fails on every account to be consistent with the observed nature of the universe.
The book is easy reading and can be finished in a day or so. The only thing I would say critical of it, is that Stenger's style of prose is very plain, and comes across as a kind of dry college lecture. In other words, he lacks the ability of a Sagan or a Gould to bring popular science to life and draw the reader in. But given that some people find the work of authors such as Harris and Dawkins too vitriolic or find Dennet's latest too academic, then this might be a book somewhere in the middle.
To get an idea of how the book is laid out, you can click here to see a chapter by chapter summary of arguments from Stenger's home page. For a fuller review, here's the eSkeptic take on God: The Failed Hypothesis.
And for the polemical, A.C. Grayling gives a glowing review of God is Not Great: How Religion Poisons Everything by Christopher Hitchens. Slate offers 3 excerpts from the book, starting here.
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