Yet more apps that have made my "why doesn't OS X do this natively?" list are Mac Shutdown X and Mac Restart X. The concept of Mac Shutdown X is simple: shut down a Mac automatically based on various kinds of events, such as a download finishing or a file disappearing. While the list of usable events is slim at the moment, the developers state on their product site that they're very open to suggestions. Mac Shutdown X can shut down on a schedule, just like OS X's Energy Preference Pane, but you can also use a calendar and clock to specify a specific date and time in the future for shutting down. Conversely, Mac Restart X does exactly what you might think: it allows you to set a schedule or specify a date (but not events - yet) for automatically restarting your Mac.
While I'm sure some people could find these separate apps handy in various ways, the fact that they sell for $10 each makes me think they should simply be combined into one utility for one price. Regardless, it's a good niche to have filled by a simple little to-the-point app.