The Ruby Language FAQ. Frequently-asked questions concerning the Ruby programming language
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.
The Ruby Hacking Guide (or maybe here; looks more current). An English translation from the original Japanese version. The RHG is a book that explains the internal workings of the official C implementation of the Ruby 1.8 interpreter.
Learn to Program. A tutorial for people with little or no programming experience. Learn basic Ruby in the context of simple programming
constructs.