[pjmlp]

I work on that type of environment, and I would stay with Java.

You might have some luck with Groovy, but the performance hit might be an issue, depending on which types of applications.

On a former project I've found out it was easier to sell the Groovy than Python, due to the syntax being almost the same as in Java.

As for .NET I would only use it if you are only targeting Windows. Mono is not really an option for heterogeneous environments in the enterprise world, plus there are a lot of FUD discussions around it.