Programming Ruby, The Pragmatic Programmer's Guide
by Wojciech Adam Koszek
Really good book which I’ve picked up after my exposure to Teach yourself Ruby in 21 days
The accompanying the book is the archive of 1600+ examples in the source code form, which I’ve written about here:
https://www.koszek.com/blog/2015/09/01/the-single-biggest-collection-of-ruby-scripts/
Worth to note: 50% of this book is API reference. Initially I didn’t like that, but now I feel like it’d be a good opportunity to go and create some Anki sets from this reference for further revising.