[eluser]jedd[/eluser]
Hi brainer.
I haven't used this directly myself, but the developers I'm working with at the moment just settled on beanstalkd / pheanstalk as a lightweight queue.
We did look at a few others - rabbitmq being the obvious one, as well as Amazon (we have a lot of AWS services already) but the former was just too heavy and the latter was just too expensive for the quantity we were looking at. You have to shard beanstalk, as I understand it, at least to an extent - a bit like how you'd use a memcache cluster I think.
Certainly worth a look, anyway. Don't believe there's a CI library ready to go, but it should be pretty easy to write your own library for it I'd think.