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
I Love Ruby Get started with the greatest programming language made for humans
Ruby is an easy to learn programming language. This book describes the fundamental concepts and techniques in greater depth than traditional introductions.
Author(s): Karthikeyan A K
NA Pages
