A Little Ruby, A Lot of Objects (Brian Marick)
The goal of this book is to teach you a way to think about computation, to show you how far you can take a simple idea: that all computation consists of sending messages to objects. Prerequisites is reader will know at least one programming language, not necessarily.
Author(s): Brian Marick
NA Pages 
Ruby Programming by Wikibooks.org
This book is currently broken down into several sections and is intended to be read sequentially. Topics covered includes: Notation conventions, Basic Ruby, Ruby Semantic reference, Built in Classes, Standard Library.
Author(s): Wikibooks.org
NA Pages
Cookin' with Ruby on Rails Designing for Testability
This tutorial is intended for use with Rails 1.2.6.It has not yet been updated to support Rails 2.x.
Author(s): Bill Walton
NA Pages
