Here's a bunch of links that I've come across on HN and Google searching over the last few days. I'm learning Rails at the moment, and these links look real useful.
If you have good links of your own, please add them in the comments! I would imagine many readers of HN are interested to some degree in Rails 3, so hope you find this useful.
Videos Discussing Rails 2 vs Rails 3:
http://rubyonrails.org/screencasts/rails3
Great Rails 3 Guide:
http://railstutorial.org/book (free online, paid PDF)
List of Freely Avaliable Programming Books:
http://stackoverflow.com/questions/194812/list-of-freely-available-programming-books (many books lited, not just Ruby)
Free PDFs for your eBook Reader:
http://stackoverflow.com/questions/172380/programming-texts-and-reference-material-for-my-kindle-creating-the-ultimate-re (again, several flavours available)