An Invitation to Ruby - Many links, review, comparison to other languages, code samples. JRuby - A Ruby interpreter written in Java. Many useful, interesting scripts, patches, extension modules, and documentation. Ruby Tuesday - Interview with Programming Ruby authors. The Pragmatic Programmer's Guide - First English language book on Ruby, by Addison Wesley Professional.
Book is available as downloadable HTML and XML files.
Ruby FAQ - Questions and answers about the Ruby programming language. The last two combine text examples with the online interpreter to run them. Com - Open discussion forum for everything Ruby. RWiki - A wiki on Ruby, written in Ruby, with separate and intermixed Japanese and English pages. Whether you speak Japanese or English, you can edit these pages.