For years Windows has had a feature called "Scheduled Tasks" this offered the ability to schedule events easily in the Windows environment.
While you can use iCal for some scheduling tasks, this is not an ideal approach.
Scheduler is a great utility which brings the ease and function of Windows Scheduled Tasks to Mac OS X.
The program is very simple and easy to use, I've only used it for a day now, but in setting it up and testing it out - it works flawlessly for me. I am so very excited to have stumbled upon this little gem. While it is freeware, I'll be donating a few bucks to support the cause.
If I can nitpick, I'd prefer the Scheduler have a look which is more inline with other Mac programs, but it's not a bad interface, and it works well.