which functional language to learn?
rosejn: Clojure.  Without a doubt.  It's by far the easiest and most productive Lisp around right now.  You get a modern core library with great support for concurrency, and you can use Java libraries with ease.  The new Clojure book published by the Pragmatic Programmer guys a pretty good read, and it gets into the important aspects of functional and concurrent programming.  I've been having a blast so far.