Programming language power and 10 years to mastery
DougWebb: I also recommend "Javascript: The Good Parts". It and the jQuery library can teach you a lot about how Javascript is really a functional language with more in common with Lisp than with C++ or Java.A second excellent book is "Higher Order Perl", which shows how Perl, also, shares a lot more in common with Lisp than most developers realize. I'm on my 13th year as a professional developer and 27th as a hacker, and I still find some of  the concepts in HoP challenging.I would also recommend learning XSLT. It's pure declarative, side-effect-free programming. If you're used to procedural code (including OOP), or even functional code, you'll still have to reattach your head sideways to learn to use XSLT effectively. It's well worth the challenge; there are problems that would be very difficult to handle in other languages which XSLT handles with ease; it's a powerful tool for your toolchest.