Here you will find pointers to manuals, tutorials and references that will come in handy when you feel like coding in Ruby.

Getting Started

Try Ruby!
An interactive web-based tutorial for beginners by Why the Lucky Stiff. No need to install Ruby, this tutorial allows you to type Ruby code right in your Web browser!
Learn to Program
A wonderful little tutorial by Chris Pine for programming newbies. If you don’t know how to program, start here.
Ruby in Twenty Minutes
A nice tutorial covering the basics of Ruby. From start to finish it shouldn’t take you more than twenty minutes.
Ruby from Other Languages
Coming to Ruby from another language? Whether it’s C, C++, Java, Perl, PHP, or Python, this article has you covered!
Learning Ruby
A thorough collection of Ruby study notes for those who are new to the language and in search of a solid introduction to Ruby’s concepts and constructs.
Ruby Essentials
Ruby Essentials is a free on-line book designed to provide a concise and easy to follow guide to learning Ruby.
The Ruby FAQ
A general collection of questions and answers useful for learning Ruby idioms or just the Ruby way of approaching typical programming challenges.
Things Any Newcomer Should Know
A page from the Ruby Garden Wiki explaining a few things “any newcomer should know.”
Ruby & Ruby on Rails programming tutorials
A site that aims to provide well-organized, rich content tutorials for both Ruby and Rails.

Manuals

Programming Ruby
The seminal work on Ruby in English, this first edition of the Pragmatic Programmers’ book is available for free online.
Why’s (Poignant) Guide to Ruby
A work in progress by Why the Lucky Stiff, filled with talking foxes and chunky bacon, this little book is well on it’s way to becoming a Ruby classic.
Ruby User’s Guide
Translated from the original Japanese version written by Yukihiro Matsumoto (the creator of Ruby), this version, by Goto Kentaro and Mark Slagell is nice overview of many aspects of the Ruby language.
The Ruby Programming Wikibook
A free online manual with beginner and intermediate content plus a thorough language reference.

Reference Documentation

Ruby Core Reference
Pulled straight from the source code using RDoc, this reference work documents all of the core classes and modules (like String, Array, Symbol, etc…).
Ruby Standard Library Reference
Also pulled from the source code using RDoc, this reference work documents the standard library.
Ruby C API Reference
Documentation for Ruby’s underlying C code. Great if you want to write C extensions or contribute to Ruby’s development.

Further Reading

Ruby-Doc.org maintains a comprehensive list of English documentation sources. There are also plenty of books about Ruby. Over on the Ruby Garden Wiki there is an assortment of user contributed content. If you have questions about Ruby the mailing list is a great place to start.