• 24 extremely useful ruby gems for web development
• Ruby User Guide
• Programming Ruby, The Pragmatic Programmer’s Guide
• PHP to Ruby
• Things That Newcomers to Ruby Should Know
• PLEAC Ruby

Framework

• Sinatra Cookbook
• Padrino Framework

Ruby on Rails

• Ruby on Rails tutorial — Learn Rails by Example
• Dresssed — the most gorgeous, complete and flexible themes you’ve ever used, or it’s free.

Data

• virtus — This is a partial extraction of the DataMapper Property API with various modifications and improvements.
• YAML for Ruby