Ask HN: Suggestion on Ruby programming books to learn advanced concepts?

I am looking into learning more about Ruby. I am already well versed in the basics of the language and have written various scripts and assorted easy stuff, just through my knowledge gained by Google and Stack Overflow, etc... But I am looking into getting more serious with the language, and wish to learn more about the concepts and advanced Ruby programming to start programming full-featured applications with it. I really hope to try to master Ruby itself before I move onto Rails, so I am looking for a real Ruby programming book that you would highly recommend. If you have any Rails books that you would recommend, please recommend them too!

So, any recommendations?