A simple list of resources for beginner rubyists. Could be useful if you're just running a mentoring session or similar to get people who are new to ruby up to speed.
Try Ruby. Written by codeschool, basic Ruby in the browser. Even has some artwork from Why's Poignant guide..
Ruby Koans was written by Jim Weirich and Joe O’Brien, it's a great intro to Ruby, delivered TDD style
The Ruby Track More coding in-browser challenges
Ruby Warrior. A prettier version of Ryan Bates' ruby-warrior. It doesn't have the scoreboard / code sharing version though like the ruby-meetup-resources one does.. Also, it suffers from the fact that you're not in your natural coding habitat. That said, it's great fun!
Ruby Monk Another interactive platform with a general intro to the language