I would also recommend https://pragprog.com/titles/ruby/programming-ruby-2nd-edition/ as well. It's a good idea to understand the language rails in written in.
The first book I would recommend is Agile web development 2nd edition. No doubt that it's the bible and the best starting source. But after reading this book and starting coding you will find that you must learn ruby to understand Rails. Someone on IRC ( ruby on rails channel) recommend me and it was the inflexion point to start learning Rails. I'm talking about the book Ruby for Rails that explains the Ruby language from the Rails point of view. Great book.
Ruby for Rails Manning black book - Ruby for Rails
