I really like Brian's way of teaching Ruby, and plan on recommending this book widely. (I may need to just buy a stack of copies to give out at work.) This is one of the best books from the 'Facets of Ruby' series by the Pragmatic Programmers.
My favorite feature of the book is the incremental approach. In the first two sections ('The Basics' and 'Growing a Script') he writes a very pragmatic chapter showing how to do something, then a 'referency' (I know, it's not a real word) chapter that goes into more depth about the concept just introduced. The third section ('Working in a World Full of People') follows the pattern less strictly, but still pulls in both the pragmatic and the reference material.
If you're getting started with Ruby, or know someone who is, this is a great book for you.