Envy Labs just released Rails for Zombies. This site is meant to help you learn Ruby on Rails in a fun, interactive way. On its own I find it to be a bit too high level. That is, with out other suplemental materials used in conjunction there isn't much context in the way of what Ruby on Rails is, how it works, and how to create a project of you own.
That being said, I went through the Rails for Zombies lessons as I went through Michael Hartl's Ruby on Rails Tutorial. You can purchase it in several formats or read it for free by clicking the on the 'Book' link. After having been through eight or nine chapters of Michael's tutorial Rails For Zombies really helped solidify my understanding of the rails stack and introduced some concepts that I hadn't seen before, like how easy it is to render xml and json.
If you're trying to learn Ruby on Rails I would strongly suggest both Michael Hartl's tutorial and Rails for Zombies, with Rails for Zombies used later on in the learning process.
What are you experiences with learning Ruby on Rails? Have any suggestions of quality RoR learning materials, let me know?