We implemented our own simple hypermedia based message queue which I have just made public here. Check the readme to get the gist of what goes on. It was not built for public consumption yet, so caveat emptor!
We have been using it in production for well over a year, and we never need to check it.. "it just works" (tm). The deployment story is not great at the moment, the plan was to get into a deb that can just be apt-get installed. So you may want to fork it and make changes if you want to use it.
We have clients for both ruby & clojure
Also another alternative we have moved to is Kafka which is a distributed log. Not as simple to setup, but the components are free (zookeeper & kafka broker). Also the clients pull data from the brokers just like in a REST system, so you can achieve the same "restart where you left off" if the system fails. You can implement all types of message patterns (pub-sub, competing consumer etc).. all the complexity is pushed to the clients like in good RESTFUL system design.