I asked a very close trusted friend for a recommendation on a Ruby book, if I could only have one book which one should I get. His response was "The Pick Axe Book".
He was 100% correct. I already know, Java, C, C++, Python, Erlang, Bash and all the Microsoft languages. This book was perfect, it told me what I needed to know without being too introductory and patronizing and without being overly assumptive that I already knew what they were explaining.
If you can only have one Ruby book, get this one!