Gearman looks decent, though it does not have persistent queues, and relies on an external storage such as an RDBMS to provide that. Not sure if there is that much gained. Still makes the database a SPOF, for example.
It depends on the database back-end you use; it can use libmemcached which opens up the possibility to use a CouchBase cluster if you really need to go that far.
Forgot to say that a decent job manager should be sufficiently composable that you can integrate a GUI and high-level monitoring into it by exploiting its API.
I consider the persistence layer a private implementation detail of a system. If Gearman controls an RDBMS schema, for example, I don't want to bypass Gearmen to mess with that directly, ever. But as far as I can see, German doesn't have an API to access anything in the queue.
