[1letterunixname]

There should be a distinction between a work queue and a job scheduler. The work queue dispatches jobs but doesn't know enough to retry them while the scheduler decides what to retry.

In Rails land, I would opt for Backburner over the commercial choices because it uses beanstalkd. For anything requiring HA, I would look at some sort of queue using an ESB as a transport. Short of HA, shard for LB.