I'd go with practical and diverse if possible: Clojure, JavaScript, and C. With clojure/JVM, you get a Lisp as well as good knowledge of java interop / apis, s

I'd go with practical and diverse if possible: Clojure, JavaScript, and C. With clojure/JVM, you get a Lisp as well as good knowledge of java interop / apis, so you'll be able to work in Java if you have to, plus you get all the java libs, and there's basically a java lib for anything you could ever want to do. Then I'd make sure you know JavaScript, its gotten to be a good enough general purpose scripting language, plus you'll be able to do anything you want browser side with it. As your third I'd pick C since basically every other modern language / OS / low level lib is built on top of it. But it depends on how much you want/need to go down to that level. If you're just going to be doing web/mobile service development I might say go with something like Go, since it'll be more practical there.