Webmin has a module for managing cron jobs and there's also a cluster
version for managing them on several systems. You can create, edit,
delete and enable/disable any cron job on the fly.
It should be easy to write a shutdown cron job, or better yet, a
tuxonice hibernate.script which suspends to disk. That way if your
system was doing something important when the cron job runs, you won't
lose the work.
Is that kind of what you're looking for Bryan?