Reddit mentions of Backpacking Pennsylvania: 37 Great Hikes

I love the Adirondacks, like the other poster suggested, but they are FAR from PA--depending on where you are in NE PA, they could be over 6 hours away.

There is some good backpacking in PA. Loyalsock trail (especially the 20-mile Loyalsock Trail-Link Trail Loop. A great 1-2 nighter, with many pretty cascading brooks and overlooks. VERY steep ascents and descents. In North-central PA, there are the Quehanna, Donut Hole, and Susquahannock Trail systems. Plus there is the Black Forest Trail and MidState trails. Even futher west is the Allegheny Nat. Forest.

There are probably 1000s of miles of backpacking and hiking trails in PA. Here's a good book: http://www.amazon.com/Backpacking-Pennsylvania-37-Great-Hikes/dp/0811731804

I would recommend that Loyalsock-Link Loop trail. It is great, but do buy the map and guide for it (or any other trail you do). If you don't have an REI or EMS, Cabella's (or Amazon) might have that stuff. You can begin and end the loop at World's End State Park, which makes for easy parking and access. You might even be able to buy the guide at the park, I think I bought my copy there.

North-central PA has a lot of options in the PA Wilds. The Loyalsock Trail, the Old Loggers Path, the Black Forest Trail, the Susquehannock Trail System, the Chuck Keiper Trail, the Donut Hole Trail, the Bucktail Path, the Allegheny Front Trail, etc.

I've found this book to be invaluable for planning PA backpacking trips: http://www.amazon.com/Backpacking-Pennsylvania-37-Great-Hikes/dp/0811731804