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Which Programming Language Should I Learn?
So far, I have played with PHP, Javascript, C/C++, SQL, ASM and VHDL.
My goal being to learn new paradigms, language constructs, etc., what language should I learn next ?
A functional language like Lisp perhaps ?
How about Python? A dialect of Lisp, Common Lisp or Scheme? Or, for pure functional fun, I hear a lot of good things about Haskell, which from my own experience has a steep learning curve.
Python will give you clarity of vision. Haskell will give you vision of clarity. Learn both.
If you want to have a lot of fun, learn Ruby next. Notice I didn't say Ruby on Rails, just start with Ruby. Its a great language that is fully OOP. Even what are considered basic types in other languages can be extended in Ruby.
I find myself using it a lot when I need to automate little tasks or get something done quickly. Of course, Ruby on Rails or Sinatra would both be great next steps if you want to work build websites with Ruby.
If you're trying to learn something new and commonly used, go with Perl or Ruby.
If you're trying to learn something completely different, but maybe not used as much, try Lisp/Scheme.
You could push yourself hard and learn some assembler. There isn't a lot of use for it these days but it's good for academic purposes. A basic understanding of assembler can teach you how a CPU works, which is valuable in any language.
As far as new paradigms go, have you considered a .net language such as C#? It's very similar to Java as well but there are some key differences in the language that are pretty interesting.
I hope this helps, good luck!