Card counters guide to casino surveillance
aka "Cellini's book". This is a high priced book with very valuable information, IMHO. It is worth the price if you are playing green or higher and play more than occasionally. On the value scale, I would place it below several other books including PBJ and BJA, meaning that those other books are severely UNDER priced for the value of the information they provide.
If you have limited resources, I would advise getting BJRM before buying Cellini's book. Of course, if you have limited resources then you will not be playing green and will probably not need Cellini's book in the first place.