ZeroMQ is a great, lightweight message broker that's getting a lot of attention because of the way it forces developers to reassess what a message queue should be, and rewards you with major performance gains if it's a good fit.

Camel users now have a much easier method for taking advantage of this tool with the release of Camel 2.11.  The new Camel/ZeroMQ component  lets you consume and produce messages using ZeroMQ.  It uses Akka for the driver:

This component uses Akka for it's Zeromq "driver" but does not use Scala Actors. This means the component does not require the JZMQ libraries to be built and present, just the native ZeroMQ library that is installed when you build ZeroMQ on your system.
http://camel.apache.org/zeromq.html

You can still use the JZMQ library if you think it will help the performance.

There's also a way to couple ZeroMQ and Mule ESB.  You should go to this blog if that interests you.