In Pennsylvania to visit my brother, so we went to get cheese steak today at Tony Luke's. Here's a pretty accurate recipe for authentic Philly cheese steak, courtesy of Pat's King of Steaks. People have almost religious arguments here regarding which is better, Pat's or Tony Luke's.
Here's more information:
So what else is Philly known for culinarily? Apparently soft pretzels and Italian sandwiches (hoagies). See: http://www.bg-map.com/foods.html