Here is a collection of the links I use regularly:
Ruby Links
API Dock's Ruby Page. Full documentation of the Ruby language with examples: http://apidock.com/ruby
Nice tutorial on how to calculate a factorial recursively: http://natashatherobot.com/recursion-factorials-fibonacci-ruby
Rails Links
The Official (Ithink) Rails Page. Full documentation of the Rails framework with examples: http://guides.rubyonrails.org
API Dock's Rails Page. Full documentation of the Rails framework with examples: http://apidock.com/rails/browse. I think they are a mirror of the official API (http://api.rubyonrails.org/) doc but Google tends to find API Dock.