We're currently using Apache Kafka which is working out great, but does include a broker as a middleman. This is good for us since it's designed to accumulate unconsumed data (or even roll it back) and still provide good performance - rather than having that happen on the producers or consumers.

It would be cool to see some stats on throughput and latency relative to # of producers / consumers and amount of data currently accumulated in the producers (since there is no middleman).