There is a scheduler2 in cvs HEAD
that offers some enhancements.
I can't say I've looked at it.
I am actually using the ScheduleManager packaged with JBoss-3.0.3.
It allows to configure multiple schedules and it works very well, but there is no real cron like facility.
I don't think it's very hard to add a cron syntax to this module. It seems to be just a question of configuring the timer notifications correctly.
I think there might be a cron like implementation in the CVS already somewhere (perhaps in contrib/varia). You should check CVS logs of Michael Bartmann, I'm pretty sure the implementation came from him.