Remember that our focus isn't to make 15 new startups in a city over a weekend, our focus is really education. We believe in "experiential education," or that the best way to learn something is by doing it.
That being said, many real companies have come out of Startup Weekend (and many many more have come out of people meeting or working together at Startup Weekend).
But, a quick list off the top of my head: Zaarly, Foodspotting, Rover, Tioki (formerly DemoLesson), Tapin.tv (YC S12), LaunchRock, Scanadu.
My cofounder and I knew we wanted to work together after attending a startup weekend and started Customer.io . During startup weekend we built a wifi / power outlet finding mobile web app.