An all-day (9-5ish) introduction to Ruby and Rails with Chad Fowler and Marcel Molina. This tutorial would provide an excellent grounding for those just getting started, or those looking to delve a little deeper into Ruby.
Mastering Rails means learning the Rails APIs, following best practices and keeping up to date with the latest changes to the framework. The most important step to mastering Rails, though, is mastering Ruby as well. To become a Rails expert you need to be at ease with the Ruby language idioms on which it is built.
This tutorial will be a tour of the core Ruby language beyond the syntax into the idioms and approaches that make Ruby (and by extension Rails) so powerful.