I dont think there any books available for cq5 yet. But CQ5 documentation is pretty good.
on http://dev.day.com/docs/en/cq/current.html you'll find the equivalent of a 4.7 inch book worth of information
with one big advantage: you can leave a comment on whether or not you liked the info and if it was helpful or not. We also appreciate feedback about how we can improve the experience for you.