"Metaprogramming Ruby" is really great. If you are an experienced programmer (especially with Lisp, Smalltalk, Haskell etc knowledge) I would recommend getting

"Metaprogramming Ruby" is really great. If you are an experienced programmer (especially with Lisp, Smalltalk, Haskell etc knowledge) I would recommend getting comfortable with the basic syntax and then diving straight into this book. It really cuts to the chase as to why ruby really is such an interesting language, something which I felt an entire read through of the pick-axe didn't really accomplish.