Check out my web site for info on regional roads - http://www.MotoRoads.net
There is nice riding in the southwest (Laurel Highlands area near Ligonier, Donegal, Somerset, Bedford).
There is nice riding in the mountains that run north/south up the middle of the state.
There is nice riding north of I-80 in north-central PA.
That's starting to sound like a big loop. If you enter PA via southeast OH and northern WV, you've got some great riding there too.