This is a short little book (only about 90-100 pages) that makes a great case against religion. To be completely honest, I may be biased as I was already an atheist, but even still I think the points in this book were well-written, reasonable, and intelligent.
Although most of the arguments are addressed to Christians (specifically American Christians) I think they can be applied against any religion.
Some may think this book is bashing and mean spirited. I disagree. There is a fundamental difference between attacking religion and attacking religious people. Harris never stoops to the low level of making personal insults. Rather, he challenges the ideas that religious folks subscribe too. Understanding this difference is key to reading this book without getting pissed off.
I think you should read this, especially if you're religious. It may not completely change your mind, but it will get you thinking.