Had to be a satellite or a spent rocket stage. The Space Station (not the Shuttle) flies SW to NE or NW to SE.
Satellites in low polar orbits (N to S or S to N) are generally earth observation craft, They are the ones that give us all those "Google Earth" images, some weather birds, and of course spy vehicles. Some are "sun synchronous" meaning they pass over the same places on Earth at the same time every day. That can be very useful for crop surveys, flood monitoring, and things that rely on similar sunlight angles for every observation.
