I have often wondered why not use a MySQL table as a "queue" (or more tables if needed). Basically, you get great performance (MySQL is really fast), you get great language support (a LOT of languages can add tasks via simple SQL) and you get such things like easy backups and replication.
According to Mike Malone the official name for a queue built on top of a MySQL table is a "ghetto queue". I believe Flickr still do all of their queuing in that way.
