I had a chance to try akka-zeromq module last month in order to implement solution for inter-service communication using Scala, Akka 2.0 and ZeroMQ.
If you ever wrote production multi-threaded server in Java you know how it is difficult to implement load balancing between worker threads. You need to fight many issues to have good load balancer:
ZeroMQ might tremendously help you with solving all these problems and much more. ZeroMQ is a high-performance asynchronous messaging library. It is native, but it has bindings for many languages and to be fair it is worth the hassle of dealing with native code.