I haven't fished some of these in quit some time. I can tell you though that the next time I fish the Letort I'll be in full camo! The fish in that stream have to be the spookiest fish I've ever went after. I consider myself pretty lucky to land a few.
I have fished the Susquehanna River just north of Harrisburg and it's some of the finest fishing for Smallmouth Bass you'll find anywhere. Never fished it as far north as Bloomsburg but since it flows right next to the fairgrounds you'll find me there in the evenings before the rally starts if conditions are good casting my 6 weight.
PA has some of the best trout fishing in the country, there are more trout streams in this state then just about any state I have fished and have fished in most.
Just a little advice for those packing their flyrods; depending on how the summer conditions will be, could influence what you should go after. Most of the time summer isn't ideal for trout fishing. If we're having a hot dry summer, streams will be very low and the fish will just be surviving, not a good time to be fishing for cold water species. This is the time to go for Pennsylvania's warmwater species. Smallmouth and Largemouth abound. The Smallmouth in particular will give you a fight on a flyrod that you can't believe. Land a 3-5 lb smally and it'll be something you'll remember for a long time.
Lot's of good info at http://www.paflyfish.com/
The Susquehanna smallmouth have been way down for the past few years. I don't know if it'll be back up this year or not. There are a number of guides that work it.
You're right about the Letort--it hasn't been stocked for years, so they're all stream bred. But there are 10 lb browns in there. It runs about a mile from my house.
Another option is to hire a guide and striper fish on Raystown Lake.