Course Correct amazes everyone who sees it. The user picks what classes are options to take next semester ("three 200-level computer science classes"), and then gives preferences for how to arrange the schedule ("nothing before 11:00 am"). The application will produce the perfect schedule in seconds.
I first attempted this as a freshman at the University of Vermont, where my programming background let me craft the entire application before discovering my knowledge of algorithms just wasn't good enough to make it work efficiently. Generating schedules from real data would've taken hours on high-end servers.
As a graduate student four years later, I tackled the problem again, refining algorithms in my sleep until the program could produce class schedules from hugely sophisticated requirements in just seconds.
You'll find tons of information about the project here, including the original project proposal, progress reports written irregularly, and even a demo of the latest version.