Lingon

At some point Apple made the decision to deprecate cron.  They replaced that functionality with launchd & launchctl.  I recently found a gui app that simplifies the process of interacting with launchd & it is called Lingon.

It has a clean interface and straight forward options.  For individuals that need a little extra help there is a wizard you can use via the "Assist" button.  The wizard will ask a few questions, ask for some input based on the way you answered the questions and generate the plist file you need and launch it, if you configured it to launch.

Take a look at it over at Sourceforge.