My origional and expanded review is located on PsychCentral.
How smart are animals? We know that dolphins are smart, but did you know that some ants are incredibly smart and teach each other new routes? Elephants can remember the voices of fellow elephants years after they've died and elephants can recognize another elephant from their skeleton alone.
Each chapter in this book is devoted to a specific type of animal, starting with ants, and then going into fish and more complex vertebrates. Intelligence is described in each of the critters.
What do the animals have in common? They are all social. Apparently, it's more social groups require more intelligence than most other things.