Maybe one of the best ways to learn a new programming language is playing with it. Nowadays if you don't code in Ruby you aren't cool. I have to recognize that programming in Ruby is funnier than in other language and for the moment I don't have anything bad to say about it.
Well, I want to introduce Ruby Quiz. It is a collection of minigames prepared to learn Ruby (or to improve your skills). Every week they publish one game, and if you are brave you can send your solution to them and it will be public. I think it's one of the best ways to learn because you can compare solutions and find were you are weak in Ruby and redo your solution doing it smarter.