Best partner language for Java -- Python, Ruby, or X?
m0digital: Ruby and Python are both great choices like everyone has said. However be warned!  It may make you quit your enterprise software job.  Once you move to a dynamic language you will become increasingly frustrated with the inadequacies of the Java language.  Eventually you'll want to work with Ruby/Python/etc so much that it will make you quit your job....and move on to something, possibly, better. :)