Why I Became an Atheist: A Former Preacher Rejects Christianity - John W. Loftus
I read this book immediately after I stopped believing in God and it is the by far the most comprehensive book against Christian apologetics I've ever seen.
It is long, but it's well written and covers everything. It could even be read as a reference book since each section covers different arguments.
Since reading that, I have never heard a Christian argument that was not covered in great depth in that book (except for some fringe conspiracy theory stuff).
The paperback is only $6 on Amazon right now.
There are a lot of great resources out there and many of them cover the same stuff, but I guarantee that, if you read this book, you will have answers to 100% of questions even the most studied Christians could throw at you.