Gadgetopia

I recommend XSLT (a logical declarative language like Prolog) and XPath (a functional declarative language like lisp). However, I suspect you have already used these, but just didn't list them. XSLT/XPath certainly uses a different paradigm than OO procedural languages.

I know XPath up, down, and sideways.

I expend a great deal of effort trying to avoid XSLT.

Another one would be Clojure http://clojure.org/

I'm working through F# & Haskell, trying to get my head wrapped around the functional language stuff. Scala would be my vote if it was just the list you have here.

I'd recommend Fan (at http://fandev.org ). It compiles to either Java bytecodes, .NET bytecodes, or JavaScript to run in your browser. It's got a really sane language design (mostly :-) ) coming from mainly from Java and C#, but borrowing bits from Smalltalk, Ruby, and some of the functional languages. But it REALLY doesn't feel like a "Kitchen Sink" language... they've worked very hard to clean up the various ugly bits of Java/C# so it's really nice to work with. Interestingly, it's still in the "development" stages (they haven't tried to publicize it too much) so I feel like you can still make meaningful contributions to the language design... it's not set in concrete.

Learn Scheme by working your way through the classic SICP, then learn JavaScript. Use JavaScript like Scheme; do the SICP exercises in JavaScript once you've done them in Scheme.

Why: because JavaScript is the most practical functional language out there. Once you know it well, it's completely useful to your day job, and using it as a functional language (instead of a completely procedural one) makes it really useful.

Haskell is also good to have fun with, and F# is probably more useful than the average functional language.

But seriously. JavaScript, man.

I recommend COBOL. I mean, with COBOL 2002 you get OO, so it's just like C#. :D

Haskell is probably the one I'd seriously recommend. I know I can't wrap my head around it, so I'm always impressed by one who can.

Or go for Ada. Remember, an Ada program compiles, it works. It's the compiling that hurts ya...

From your list, I'd Lisp or Erlang. Anything in that list would be great to learn, generally more for the experience with a different paradigm and not practical usage, but a lot of stuff is written in both Lisp and Erlang so you might actually have a real use for them in the future in addition to the learning benefits.

I learned a small amount of Lisp (very, very small) my first semester at UNL as it was being taught to non-CS students (mostly incoming freshman who thought they were taking a class on Office). I enjoyed it. Same with Forth. Prolog, on the other hand, confused me. I wasn't a huge fan, but that could be because very little was taught and I'm used to learning more about a language than the very basics.

I'd suggest F# - Microsoft's implementation of OCAML on the .Net framework. Whether or not functional programming proves to be as popular as some pundits predict, if you're going to do it, you might as well do it on a ubiquitous platform.

I fondly remember coding in Snobol in college. Not the most practical language, but if you are looking for something different.

Either way, keep us posted on what you choose and how it's coming along... Might be an interesting experiment to take on myself.

Actually I would strongly recommend learning assembly. I think you'd enjoy. From there you can more easily try pretty much anything.

I second clojure. Check out Programming Clojure by Stuart Halloway