Robb Wolf's book is great for pure paleo, and easy to read while still getting great info. The Paleo Answer is another great one, but a little more wordy.
In other words if you geek out on science get paleo answer. If you or someone you know is just on the fence and you wanna nudge them in the right direction without putting them to sleep give them paleo solution by robb wolf.
Another book I suggest is "the dark side of fat loss" by Sean Croxton, he follows paleo, but goes into great detail about many things such as stress, hormones, digestion, and all kinds of lifestyle factors that are easily as important.