Looking for books from which HN'ers read not just for enjoyment, but directly taught them how to do something.
The ggplot2 (viz for R) book has been great: http://www.amazon.com/ggplot2-Elegant-Graphics-Data-Analysis/dp/0387981403
Ruby Best Practices also gave me some ideas on better use of blocks to do data processing from files: http://blog.rubybestpractices.com/posts/gregory/022-rbp-now-open.html