Clojure
I'm prejudiced against JVM. I wouldn't let that stop me, but more than one person has quoted access to Java libs as a plus.
Go
The "Go way" demands lots of boilerplate. C with libs for concurrency, comms and GC would be more concise. It was very promising until I realized this.
Erlang
It is my primary concurrent language. I just don't write using concurrency as much as I should.
ECMAScript
For want of a satisfactory implementation.
Honorable (not-so-sadly) mentions:
Python
Ideally I want strong concurrency, powerful closures, tailcall elimination and NO EXCEPTIONS. Obviously not Python.
Haskell
Tries hard to deny the machine. That's not a bad thing (except when it is) but most of my work is highly machine-relevant.
Perl
Been there, done that--what was I thinking? (Everything, apparently. All at once.)