The PDF version of Build Your Own Ruby on Rails Web Applications by Patrick Lenz is available for free for the next 60 days. Click over to Sitepoint to download the complete book (20MB). The book introduces Ruby on Rails to aspiring Rails developers by showing them how to build a Digg clone step by step. In the process it touches on many important concepts such as test driven development.
via Riding Rails
Thanks for the link. :)