Here is a list of books I read and can recommend to any Ruby-developer:

«Practical Object-Oriented Design in Ruby» — Sandi Metz.

«Metaprogramming Ruby: Program Like the Ruby Pros» — Paolo Perrotta.

«Confident Ruby: 32 Patterns for Joyful Coding» — Avdi Grimm.

«The Ruby Way: Solutions and Techniques in Ruby Programming» — Hal Fulton.

«Crafting Rails Applications: Expert Practices for Everyday Rails Development» — José Valim.

«Effective Testing with RSpec 3» — Myron Marston and Ian Dees

«Programming Ruby: The Pragmatic Programmers’ Guide» — Dave Thomas, Chad Fowler.

«Design Patterns in Ruby» — Russ Olsen.

«Effective Ruby: 48 Specific Ways To Write Better Ruby» — Peter J. Jones.

«Rails AntiPatterns: Best Practice Ruby on Rails Refactoring» — Chad Pytel, Tammer Saleh.

«Ruby Performance Optimization» — Alex Dymo.

«Growing Rails Applications in Practice» — Henning Koch and Thomas Eisenbarth.

«Refactoring in Ruby» — William C. Wake and Kevin Rutherford.

«99 Bottles of OOP» — Sandi Metz.

«Fearless Refactoring: Rails Controllers» — Andrzej Krzywda.

«Clean Code» — Robert C. Martin.

«Domain-Driven Design: Tackling Complexity in the Heart of Software» — Eric Evans.

«Implementing Domain-Driven Design» — Vaughn Vernon.

«Domain-Driven Design Distilled» — Vaughn Vernon.