Every programming language has a number of works you just cannot not read. Perl has the camel book, C++ has "The C++ Programming Lanugage," etc. Ruby does have it's own dead tree you cannot not read, "Programming Ruby: The Pragmatic Programmer's Guide," the so-called "pickaxe book," but that's covered so many places and recommended by everyone. Here are some links you must read in order to understand Ruby.
- Ruby Koans - A "koan" is a story or dialog crafted to make a student think. The story itself doesn't teach anything, the story forces you to investigate things yourself. It may make you think you have everything backwards, only through investigation do you discover something new or strengthen your understanding of something. So what does this have to do with Ruby? Ruby Koans is a really great set of koans, in this case short Ruby programs, that you must fix. Every one is broken or incomplete in some way, and you must go through, one by one, and fix them. They all teach some little part about Ruby you didn't know about before, or show a feature you already knew in a different way. This should be required for all Ruby programmers, it's that good.
- The Ruby Homepage - This might seem like a no-brainer, the Ruby homepage. But you can do more than just download Ruby here. Here you gain access to the Ruby community, among other things the mailing lists where people do nothing but talk Ruby, and the developer's mailing list where you can see the Ruby developers plotting to take over the world (by making Ruby better every day). Even if you don't have anything to say on these mailing lists, just reading is a cornucopia of information.
- Stack Overflow - In the same vein as the Ruby mailing lists is Stack Overflow. This is a site with nothing but programming questions such as What is 'taint' and 'trust?' People ask questions, people answer questions. The link above will take you to all questions tagged with Ruby. Again, even if you don't have any questions to ask, simply reading the questions and answers will expand your understanding of Ruby.
- Ruby-Doc.org - Yes, you probably have Ruby documentation on your system already. You can access it with the ri command. But more and more people don't even enable that on their Ruby and Rubygems installations anymore. It's just plain inconvenient to read it on the terminal (funny, that used to be where it was most convenient, how far the web has come!) and it's a pain to fire up that ri web server all the time, so why not just go to Ruby-doc.org? Really, when are you not online? Everything you want to know about Ruby is there.
- Ruby Inside - Peter Cooper has been slavishly updating this blog for years now. It's all good Ruby links, current events, news, and random Ruby-related things. Everything here is good reading, Peter digs through all the "other" stuff and just gives you the good links.
- Ruby Flow - Another one from Peter Cooper, but this time anyone can submit. Since anyone can submit, you do get some less "worthy" links, but it's mostly all good stuff.
- Ruby Internals presentation - This is a presentation done by Patrick Farley shows you how Ruby really works. It clears away so much of the fog and just makes you understand everything. Things like bindings and how metaprogramming works. Once you understand the basics, watch this video! Also, he's hilarious and a great presenter, I can't recommend this enough.
- Ruby Hacking Guide - Here's another work that digs real deep into Ruby. Unfortunately, it was written in japanese and only portions of it are translated into English, but the portions that are translated are pure gold. Because once you understand the basics, it's time to start peeling back layers and getting an intuitive understanding of how the language really works.