Schedule Daily Task can add daily tasks to, and remove any task from, your user account's launchd database. Tasks can be applications, AppleScript (bundle) applications, or Automator workflow applications. Apple recommends using launchd instead of cron if you have Mac OS 10.4 or later. Besides adding or deleting the .plist file which defines the task, Schedule Daily Task also also loads/unloads the task with launchctl, so that your add/delete is effective immediately.
Unlike cron jobs, if your computer is off or sleeping when the time for a scheduled task occurs, the task will run, belatedly, when your computer wakes up.
If you need more features, you might try the freeware app Lingon instead. Some people say that Lingon works. However, the reason I wrote Schedule Daily Task is because it seemed to me that Lingon has more than one bug when running in Mac OS 10.5. Schedule Daily Task is crude and doesn't do much, but it works for me.
Click on the "Support" tab to send bug reports. It's actually just a short AppleScript application, though, so if you know AppleScript, you can open it with Script Editor and fix or customize to your liking.