Clojure, people! If you haven't yet checked out Rich Hickey's new functional lisp for concurrent programming on the JVM, then you're missing out on something really, really, mind-blowingly cool! I'm a Lispnik at heart, and I do most of my personal development in Common Lisp on SBCL, but I have to program a lot of Java code for my day job. Clojure has definitely caught my eye and is #1 on my list of next languages to learn.
Check it out: http://clojure.org