Ruby Tutorials — Basics

Essential Learning for Ruby on Rails

Ruby on Rails for Designers

Be confused no more! metaclasses and metaprogramming explained with great ease.

Basic hash, regular expressions and blocks tutorial.

Speed up your program using ruby threads

Utilize the method_missing method to create dynamic methods at runtime

Quick yet effective way to clean up simplistic blocks

Extend existing ruby methods to add your own functionality while retaining previous functionality.

Commander is a Ruby Gem aimed towards simplifying the sub-command/master-command structure of many executables. (dont forget to watch the screencast)

The facets gem is packed full of common functionality that is certainly welcome along-side of the standard library. If you are not using it, chances are you SHOULD be.