As the New Year approaches a software developer's idea of renewal is typically learning a new programming language. I ran across the following post which provides some interesting alternatives to consider.
10 programming languages worth checking out:
Also, Dr. Dobb's has an article on functional programming languages: It's Time to Get Good at Functional Programming
I’ve got client developing server apps using ERLANG. Their core capability is messaging so the built in resources of ERLANG fit the bill nicely.
Consider Python. You can ‘get things done’ (thanks to great documentation and libraries) and write in a functional style if you feel so inclined (I wouldn’t call it a functional language, but it’s not incomparable to Squeak or Clojure on your list, both which allow easy state modification).
I do this all the time in Python, generally eschewing stateful objects for what would be more accurately described as composite values.
I see that you don’t have it on your list of categories already, so that’d be a good place to go, even if it is more ‘mainstream.’