I've started playing around in Ruby, a programming language that's gaining in popularity and has an elegantly simple syntax. Over the course of my explorations I've come across a few useful links, which I'll share here:
Ruby - Official website for the Ruby programming language.
Ruby on Rails - Official pages (including much documentation) for Ruby on Rails, a framework that simplifies web database application development.
Programming Ruby - The Pragmatic Programmer's Guide: First edition of the book, full-text free online.
Programming Ruby - The Pragmatic Programmer's Guide: Second edition of the book, available for purchase.
Mr. Neighborly's Humble Little Ruby Book - the PDF version of this book has just been released for free, and it's a very easy read.
Linux Journal review of The Ruby Way - review of a book on Ruby.
Rolling with Ruby on Rails - A short tutorial to help users install Ruby and Rails, and then create a short, web-enabled database-using program via Ruby on Rails. I was able to follow this with only minimal changes in Ubuntu, and learned a bunch in the process.