Books for advanced ruby learners

I wrote a book list for ruby beginners some days ago, now I will make a list for advanced ruby learners:

Practical Ruby Projects -- Ideas for the Eclectic Programmer

Apress
2008
by Topher Cyll
304 pages
This book covers 8 projects, including a music player, a game, rubycocoa project and a project implementing Lisp.

intermediate ruby learners who want to get their feet wet with practical projects.

Ruby Phrasebook -- Essential code and commands

Addison Wesley
2008
by Jason Clinton
Teach you how to do something with short simple code. It is a pocket-size book.
For any Ruby learner or developer who want to have a cheat book.

Ruby Cookbook -- Recipes for Object-Oriented Scripting

O'Reilly
2006
by Lucas Carlson and Leonard Richardson
873 pages
This book provides solutions and discussion for hundreds of common ruby problems.

Ruby 1.8 and 1.9

Ruby Pocket Reference -- a Quick Guide to Ruby

OReilly.
2007
by Michael Fitzgerald
170 pages
This book is different from Ruby Phrasebook, instead of showing your how to finish a task with simple code, this book explains what a method does, mostly with words.

Practical Ruby Gems

Apress
2007
by David Berube
271 pages
This book starts with what is rubygems and how to install one, and then dedicates the next 200 pages to introducing more than 20 particular gems, and finishes with how to create and distribute rubygems.

FXRuby -- Create Lean and Mean GUIs with Ruby

Pragmatic Bookshelf
2008
by Lyle Johnson
211 pages
A book on FXruby, a graphical user interfaces (GUIs) library for Ruby. This book will help you building GUI applications with Ruby and FXRuby.

Data Structures and Algorithms with Object-Oriented Design Patterns in Ruby
http://www.brpreiss.com/books/opus8/
by Bruno R. Preiss
A FREE online book .This book focuses on OO design pattern and data structures.

Mainly for university students.

Ruby in Practice

Manning
2009
by Jeremy McAnally, Assaf Arkin and others
335 pages
With this book, authors share varies ruby experiences and techniques.