There's big bucks in farming (Farmville), whacking the competition (Mafia Wars), exploring the wild west (Frontierville), raising pets and dressing them up (Petville), exploring islands (Treasure Isle), and, well, hopefully by now you get the idea. Zynga's various 'villes and other social games have turned the San Francisco game company into a multi-billion juggernaut, according to an amended SEC filing, CNet reports.