From a very long time, I have been an admirer of Lisp, an often praised but seldom used programming language. Common consensus about Lisp is that it is the kind of language you don’t need to know to get your daily tasks done, but any programmer worth his salt should be familiar with its concepts.
For a beginner, perhaps the easiest way to get a taste of Lisp is to go through The Little Schemer. As programming books go, this is quite an unusual one. Programmers like to say that they don’t really learn something new, unless they have written some code in it. The Little Schemer takes this idea up a notch. There are no formal definitions (but there are some “commandments”!) and very little explanation. The book is composed of nothing but (often humorously phrased) coding problems from beginning to end. You need to fire up your compiler and start writing code from the get go. The idea is to let the readers pickup functional programming concepts intuitively rather than teaching them explicitly. You can use any implementation of Lisp dialects like Scheme or Common Lisp to work out the problems. MIT/GNU Scheme worked fine for me.
Lisp, in its original form, is hardly ever used in actual production (even though its dialects are). But it is still important to understand it because many mainstream programming languages like JavaScript, Scala, R etc. follow the functional programming paradigm. The Little Schemer is an easy and fun way to get on board!