10 Minutes to Your First Ruby Application, by James Britt. There's no better way to experience the elegance and power of Ruby than to fire up your code editor and start writing Ruby code. Create a small, useful Ruby application, and along the way, you'll learn what makes the language tick.
Try Ruby. Got 15 minutes? Give Ruby a shot right now! Try Ruby is an online, Web-based Ruby shell. And it has an interactive tutorial.