Most people are familiar with the setting a Start Up item on Mac OS X and the new Lion behavior of relaunching apps that were open at the last restart is also great. But I've also experienced the problem where I've gone away on a trip only to have iTunes crash or shutdown for some reason. That means the AppleTV is no longer able to stream SuperWhy episodes from the media Mac and that's a problem.
I have a Keyboard Maestro macro the simply checks every 10 minutes and launches specific applications if they are not running.
Now I could write a script to do the same and then schedule the script through Cron in the terminal, but why hassle. Keyboard Maestro makes it easy. I keep a "Cron" folder of macros that just run at a specific time. It doesn't get much easier than that.