0MQ

AKA zeromq, ØMQ. See http://www.zeromq.org/

This looks like a very promising way to send packets of data across a network. It would totally kick butt over HTTP based protocols such as SOAP and XML-RPC, and it seems to have nice batching as well. Of course, it doesn't look like JavaScript will support it.

RabbitMQ also seems interesting, although it is larger and more heavy-weight.